ALBERT

Notes: A new method for calculation of the radial distribution functions (RDFs) at contact from a specified hard-sphere mixture equation of state (EOS) is proposed. The method is applied to two available accurate EOS expressions and new analytical formulas for the RDFs are obtained for binary additive hard-sphere mixtures. The results of the new formulas are compared with available computer simulation data and with those of other RDF expressions from the literature. The evidence to date suggests that the new formula is more accurate than alternative formulas currently available. © 2002 American Institute of Physics.

Notes: The electron transfer (ET) process has been studied in a three sites system: the donor and the acceptor of electrons separated by a bridge. We have considered an isolated system in order to understand the characteristics of the process itself without introducing a bath. The ET process has been studied considering both the electronic and the vibrational part. This complete vibronic analysis has been done in a three electronic-n vibrational model. Two questions are put into evidence. First of all we have analyzed the relevance of the vibrational part in modifying a pure electronic description both in the electron transfer time and in the site populations. A second aspect underlined is the difference between a tight-binding system (donor and acceptor without a direct coupling) and a full coupling one. The drastic difference between these two cases has been rationalized. © 2002 American Institute of Physics.

Notes: Near-field Raman imaging of organic molecules is demonstrated by an apertureless near-field scanning optical microscope, the tip of which is a silver-layer-coated cantilever of an atomic force microscope (AFM). The virtue of the enhanced electric field at the tip apex due to the surface plasmon polariton excitations enhances the Raman scattering cross sections. This phenomenon allows us to reveal from near-field Raman images the molecular vibrational distributions of Rhodamine6G and Crystal Violet molecules beyond the diffraction limit of a light. These molecular vibrations cannot be distinguished by AFM topographic images. © 2002 American Institute of Physics.

Notes: An extended two-dimensional analogue of the Merrifield model of the mixing between Frenkel and charge-transfer excitons is used to calculate the electro-absorption spectrum of the α-sexithiophene single crystal. The model reflects the symmetry of the crystal and takes into account all the major interactions between the molecules. The input parameters are estimated from independent quantum-chemical and micro-electrostatic calculations. The simulated spectrum is in very good agreement with experiment, both in shape and in absolute amplitude. The results demonstrate that the eigenstates of the crystal between 2.55 and 2.85 eV are primarily of charge-transfer parentage, so that charge-transfer contributions dominate the electro-absorption spectrum in that region. This first successful reproduction of the electro-absorption spectrum of a single crystal is a stringent test of the theoretical description that confirms its validity. © 2002 American Institute of Physics.

Notes: We report a Brownian dynamics (BD) simulation study of the Förster energy transfer in a dye-labeled Rouse polymer chain. The simulation method is based on the normal mode BD propagation and numerical path integration of the survival probability. It is shown that a properly constructed truncated normal-mode approximation (TNMA) can speed up the simulations considerably, without essential loss of accuracy. In particular, an effective-sink TNMA scheme is found to be quite efficient. The idea is based on a standard time scale separation ansatz, where all the normal modes are separated into slow and fast, in terms of the corresponding relaxation times. The fast normal modes are assumed to be equilibrated in the course of reaction and thus can be integrated out. Their effect is to modify the reaction sink for the slow modes. The first-order approximation can be handled most easily, without a simulation. Even this simple approximation can be preferable to the well-known Wilemski–Fixman approximation, if the reaction sink is wide, i.e., when the Förster radius exceeds the polymer mean bond length, the condition often chosen in experiments on polymer folding. © 2002 American Institute of Physics.

Notes: The quantum theory of stress is developed within the atoms in molecules (AIM) framework. The complete local stress field is introduced and integrated within atomic basins, and it is shown that the kinetic term gives rise to the atomic virial theorem. The role of the potential part of the stress field in the AIM theory is discussed, and its necessary consideration in order to define atomic pressures presented. These atomic pressures are shown to tend to the thermodynamic limit as the size of the system grows. A link between the AIM theory and the theory of electronic separability has also been found. A set of simple examples illustrates our results. © 2002 American Institute of Physics.

Notes: A procedure for optimizing basis sets for core hole binding energies is described. Contracted Gaussian basis sets are optimized for ground state and core hole state atomic configurations, exponents and contraction coefficients being determined by a minimization of the atomic self-consistent field state within a simulated annealing procedure. The basis sets are used in connection with Δself-consistent field, ΔMøller–Plesset and ΔKohn–Sham theory calculations of core electron binding energies and chemical shifts of high accuracy. Whatever the method, the small basis sets optimized in this way give results with an accuracy comparable to that obtained using very extended normal basis sets close to the complete basis set limit. They provide an excellent alternative to treat large molecular systems and push the accuracy of the ΔKohn–Sham technique for binding energy computations even further, exhibiting only small (a few tenths of an electron volt) deviations from experimental data. © 2002 American Institute of Physics.

Notes: It is demonstrated that the compounds of late actinides, namely Lawrencium and Nobelium surprisingly exhibit unusual nonactinide properties in that unlike other actinides the chemistry of these species is principally determined by the 7s and 7p orbitals rather than the 5f or 6d shells. Relativistic computations including electron correlation and spin–orbit effects using the complete-active space multiconfiguration self-consistent field followed by second-order and multireference relativistic configuration interaction (RCI) techniques are considered for the Lawrencium and Nobelium dihydrides as well the atoms. The ground and first excited states of Lawrencium and Nobelium arise from the 7s and 7p shells, and thus the potential energy surfaces of these species are unusual in having considerable 7p characteristics. Both molecules form stable bent ground states reminiscent of sp2 hybridization with equilibrium bond angles near 120°. The Lawrencium compounds exhibit unusual characteristics due to avoided crossings of the potential energy surfaces. As a result of spin–orbit coupling, the 2B2 state of LrH2 undergoes avoided crossing with the 2A1 state in the spin double group, which reduces the barrier for insertion of Lr into H2. The Nobelium compounds are shown to be considerably less stable compared to Lawrencium compounds due to the relativistic stabilization of the 7s shell of the Nobelium atom. It is shown that the barrier for insertion of Lr into H2 is lowered by relativity (spin–orbit coupling), while No has to surpass a larger barrier due to the relativistic stabilization of the 7s2 shell, which is not very reactive. Lawrencium is the only element in the actinide series with unusually low ionization potential, and NoH2 has an unusually large dipole moment of 5.9 Debye. It is suggested that the Lawrencium and Nobelium compounds should have periodic similarities to the thallium and radium compounds, respectively. © 2002 American Institute of Physics.

Notes: Minimum energy pathways for the rearrangement of the anions of the water trimer and tetramer anions between their cyclic and chain structures were investigated by means of ab initio electronic structure calculations, coupled with nudged elastic band optimizations. The rearrangements of both anions are found to proceed by opening of the cyclic structure and reorientation of the water molecules as the excess electron migrates to the terminal water fragment with the dangling hydrogens. The activation energies for the cyclic→chain rearrangements are calculated to be 0.11 and 0.32 eV for (H2O)3− and (H2O)4−, respectively. © 2002 American Institute of Physics.

Notes: A transition from a fluid to a constrained phase, in dilute solutions of a rodlike molecule, poly(2,5-dinonylparaphenylene ethynylene)s (PPE) in toluene has been studied, exploring the dynamics and the structure of the PPE molecules and the solvent in both phases. The transition is characterized by visual changes in the viscosity of the system and in its color, where a transparent liquid transforms into a yellow glassy phase. Nuclear magnetic resonance relaxation measurements indicated that significant restriction of motion of the solvent and of the polymeric molecule take place as the gel-like phase is formed. Small angle neutron scattering studies have shown that in the liquid phase, PPE forms molecular solutions where the molecules are fully extended. Upon transition into the constrained phase, aggregation of PPE molecules into large flat clusters occurs. When the aggregates are too large to freely move in the solution, a transition into a constrained phase takes place. The interaction between the highly conjugated PPE molecules and the solvent results in constraint of the motion of the solvent as well. © 2002 American Institute of Physics.

Notes: In order to explore whether vacancies could trap charge-transfer (CT) states, the polarization and charge-quadrupole energies of CT configurations near vacancies in anthracene are calculated. Polarization and charge–quadrupole energies of single charges and of CT configurations in perfect crystals and of single charges near vacancies are recalculated treating anthracene as 14 submolecules at the heavy atoms, rather than three at the centers of the rings as in previous work. This improves agreement with experiment. A vacancy adjacent to either of the two lowest-energy CT configurations reduces the dielectric screening of the Coulomb stabilization, thereby stabilizing the configuration by typically 20–50 meV. However, for some higher-energy CT configurations a vacancy on or near the CT axis can actually increase the screening and destabilize the configuration by up to 40 meV. A vacancy also changes the charge–quadrupole energy by as much as ±250 meV, so that this effect dominates (as for single charges), leading to traps as deep as 300 meV for the two lowest-energy CT configurations. Such traps could reduce the efficiency of charge-carrier photogeneration by enhancing geminate recombination of CT configurations. © 2002 American Institute of Physics.

Notes: We propose a theory for the effective interaction between soft dendritic molecules that is based on the shape of the monomer density profile of the macromolecules at infinite dilutions. By applying Flory-type arguments and making use of the experimentally measured density profiles, we derive a Gaussian effective interaction whose parameters are determined by the size and monomer number of the dendrimers that are derived from small-angle neutron scattering (SANS) measurements. By applying this theory to concentrated dendrimer solutions we calculate theoretical structure factors and compare them with experimental ones, derived from a detailed analysis of SANS-data. We find very good agreement between theory and experiment below the overlap concentration, where drastic shape deformations of the dendrimers are absent. © 2002 American Institute of Physics.

Notes: A simple algebraic model is used to show that Hirshfeld surfaces in condensed phases may be understood as approximations to the interatomic surfaces of the theory of atoms in molecules. The conditions under which this similarity is valid are explored, and both kinds of surfaces are calculated in the LiF and CS2 crystals to illustrate the main results. The link between Hirshfeld and interatomic surfaces provides a physical ground to understand the usage of the former to visualize intermolecular interactions. © 2002 American Institute of Physics.

Notes: The excitation spectra of the D˜ 1Πu, E˜ 1A, and F˜ 1Σu+ states of C2H2 in the 135.3–130.8 nm range are measured under jet-cooled conditions by detecting fluorescence emitted from C2H(A˜ 2Π) or C2H(B˜ 2A′) photofragments. In the photofragment emission yield spectra, the origin bands of the D˜–X˜ and F˜–X˜ transitions are observed with Lorentzian profiles with bandwidth (Γ) of 58.9(4) and 66.7(2) cm−1, respectively. By identifying the bending progressions of the E˜–X˜ transition appearing with narrower Lorentzian profiles with, Γ∼40 cm−1, the band previously considered to be the origin band of the E˜–X˜ transition is assigned to the transition to the second overtone (v3=3) level in the near-cis bending (ν3) mode. The transitions to the C–H stretch excited levels in the D˜ and F˜ states are observed using the infrared-VUV double resonance excitation scheme. The D˜ 311, D˜ 111 311, F˜ 311, and F˜ 111 311 bands are identified at 74 334(3), 74 121(5), 74 522(3), and 74 388(3) cm−1, respectively, with much broader bandwidth (Γ〉100 cm−1) than the D˜–X˜ and F˜–X˜ origin bands, indicating that the dissociation is accelerated significantly in both of the D˜ and F˜ states when the antisymmetric C–H stretch (ν3) mode in the D˜ and F˜ states is excited. © 2002 American Institute of Physics.

Notes: The photodissociation dynamics of thiophosgene (CSCl2) and the respective branching ratios of both dissociation products Cl and CSCl have been studied by 3D imaging of the photodissociation product chlorine in its ground state 2P3/2[Cl] and excited spin–orbit state 2P1/2[Cl*] employing the resonance enhanced multiphoton ionization and time-of-flight technique at a dissociation wavelength of about 235 nm. A novel technique is applied where the complete three-dimensional (3D) momentum vector of a reaction product is directly determined. The kinetic energy distribution (KED) for Cl* is observed for the first time. The obtained KEDs of Cl and Cl* are different in the low kinetic energy range due to the correlating state of the partner fragment CSCl. In the case of ground state Cl the CSCl partner radical is produced in the ground X˜, A˜, and B˜ states with a contribution of 4±0.5%, 60±5%, and 36±3%, respectively. In the case of Cl* the corresponding CSCl is produced with a contribution of 7.5±0.5% in the ground X˜, 71.5±5.5% in state A˜, and 21±1.5% in state B˜. The yield of Cl*, φ(Cl*)=P(Cl*)/[P(Cl)+P(Cl*)], was found to be 0.47. No significant velocity dependence of the anisotropy parameter β could be observed. The mean value +0.03 suggests a decay on the B˜ (A1) surface. © 2002 American Institute of Physics.

Notes: The general problem of adiabatic relaxation, or thermal equilibration between a sample and a reservoir initially at two different temperatures, is presented. By thermostatting both the sample and reservoir, a nonequilibrium steady state can be set up to measure this relaxation rate. An accurate treatment of the coupling between sample and reservoir in the steady-state case leads to substantially improved agreement with vibrational relaxation rates obtained from adiabatic equilibration. We show that for large signal to noise ratio, the nonequilibrium simulation can be considerably more accurate than the direct equilibration measurement. We demonstrate two other examples of transport phenomena obtained from thermostatted sample-reservoir driving, namely, thermal conduction and shear flow in a fluid. © 2002 American Institute of Physics.

Notes: Time-resolved, pump–probe measurements are used to directly interrogate dissipative fluid dynamics in bulk He-II, on molecular scales, as a function of temperature and pressure. The Rydberg transitions of the triplet He2* excimers, which solvate in bubble states in liquid helium, are used as nanoscale transducers to initiate and to directly monitor the motion of the fluid in the form of damped oscillations of a 13 Å spherical bubble. The oscillations are damped out after one period, with a temperature-dependent period that directly tracks the normal fraction. As such, the bubble oscillator acts as a nanoviscosimeter. Through simulations of the observed signals, it is established that the coherent response of the bath obeys hydrodynamic equations of motion of a continuum subject to two-fluid flow. Dissipation occurs through two distinct channels: (a) Radiation of sound in the farfield, driven by the acceleration of volume in the compressible fluid; (b) temperature-dependent drag in the near-field. The drag can be considered to be strictly viscous in origin, or due to ballistic scattering of rotons from the bubble edge. The experiments do not distinguish between these two microscopic models. With this caveat in mind, it can be concluded that for these breathing modes of bubble states, the macroscopic concepts of superfluidity scale down to molecular dimensions. The simulations also yield effective potentials that describe the coupling between the compressible Rydberg electron and the compressible fluid. © 2002 American Institute of Physics.

Notes: We describe an efficient implementation of a polarizable mixed Hamiltonian model of electronic structure that combines Hartree–Fock, Kohn–Sham, or multiconfiguration quantum-chemical wave functions with a polarizable and flexible molecular mechanics potential of water, and that is applicable to micro-solvated electronic excited states. We adopt a direct algorithm for the calculation of the polarization response of the solvent subsystem. The strategy facilitates the calculation of the energy of the system and of the forces with respect to the solute coordinates and the solvent coordinates, including for excited states. This capability opens the way to the determination of optimized, transition structures, force constants, and intrinsic reaction pathways for the solute–solvent system, and to molecular dynamics calculations to account for finite temperature effects. As an illustration we characterize the structure and energy of micro-solvated formaldehyde H2CO in its ground state and in its 1(π*←n) excited state. A novel perpendicular structure is found to be the lowest energy conformation of the H2CO1(π*←n):H2O complex. The all-quantum-chemical results and the mixed Hamiltonian results, with or without solvent polarizability, are in semiquantitative agreement. We comment on the choice of Lennard-Jones parameters associated with a solute excited state. Lennard-Jones parameters that yield good ground state structures and energies with the mixed Hamiltonian model, are found to be too soft for the micro-solvated excited state H2CO in the adiabatic (equilibrium micro-solvation) regime. © 2002 American Institute of Physics.

Notes: The two lowest-lying (X and 2)1Σ+ states, the first 3Σ+, 3Π, 1Π, 3Δ, and 1Δ excited states of the AgCl molecule have been studied through extensive complete active space SCF+averaged coupled pair functional calculations, using a 19-active-electron relativistic effective core potential (RECP) for Ag, a 7-active electron RECP for chlorine and large optimized Gaussian basis sets for both atoms. The 2 1Σ+ and 3Σ+ excited states present shallow relative minima very near the equilibrium geometry of the ground state, while the lowest 3,1Π states were found to be totally repulsive in the internuclear range studied. The 3,1Δ states present very shallow minima around 5.2 a.u. The calculated spectroscopic constants for the ground- and excited states are compared with the available experimental data and have been found in good agreement. Even though the 3Π state is repulsive, it lies very close in energy to the 2 1Σ+ one near the equilibrium geometry of the ground state; thus, a strong 3Π–2 1Σ+ mixture through the spin–orbit interaction is predicted to occur that will lead to the fine-structure B state responsible for the recently revised B←X transitions in AgCl. The C–X transition observed at 43 500 cm−1, appears now to arise from a higher-lying root of the 1Σ+ or Π manifolds, perhaps the third 1Σ+ root, while the D–X system seems to arise from the 3Δ←1Σ+ transition around 49 000 cm−1. © 2002 American Institute of Physics.

Notes: The double photoionization of HBr molecules, by synchrotron radiation in the energy range between 25 and 55 eV, has been studied in a mass spectrometric experiment. The HBr2+ and Br2+ product ions have been detected by a photoelectron-photoion-coincidence technique, while the H++Br+ formation, which follows the double ionization of HBr, has been studied by photoelectron-photoion-photoion-coincidence technique. HBr2+ ions are produced with a threshold of 32.4±0.4 eV, while the dissociative channel leading to H++Br+, shows a threshold around 33 eV. The production of H+Br2+ occurs with a threshold of 40.2±0.4 eV. These results appear to be in a fairly good agreement with earlier nonrelativistic calculations of potential energy curves and also with values indirectly obtained from experimental Auger spectra. © 2002 American Institute of Physics.

Notes: The speed and angular distributions of I+ ions, produced when ICl molecules were exposed to both ultraviolet and visible radiation at 304+608 nm, 355+608 nm, and 304+532 nm, were measured by velocity map imaging. An intense central feature in the I+ images was observed to be very sensitive to the polarization of the ultraviolet light and is attributed to a dissociative ionization mechanism involving three-body fragmentation: ICl+hv (visible)+3hv (ultraviolet)→I++Cl+e−. The effect of varying the delay between the visible and ultraviolet radiation on the I+ images suggests that an intermediate gateway state of ICl reached by absorption of one photon of visible light mediates the transition to the superexcited dissociative ionization state. © 2002 American Institute of Physics.

Notes: The 364 nm photoelectron spectrum of Si2C3− is reported, together with high level ab initio calculations of the linear anion, and six linear and eight nonlinear structures of the neutral Si2C3. The adiabatic electron affinity of Si2C3, corresponding to the transition from the linear anion to the lowest electronic state of the linear singlet neutral, is found to be 1.766±0.012 eV. Theoretical results were essential for interpreting the spectrum. The level of theory necessary to accurately describe the electronic structure of Si2C3 cluster isomers is presented and discussed. Several vibration frequencies for the neutral linear structure are obtained from the spectra and compared to results from different levels of theory. © 2002 American Institute of Physics.

Notes: State-to-state and total rotational energy transfer (RET) rate constants were measured for collisions of CN(B 2Σ+,v=0,Ni=4,7,8,11) with H2, CN(X 2Σ+,v=2,Ni=4,11) with H2 and D2, and CN(X 2Σ+,v=3,Ni=4) with NO at room temperature and under single, or near-single, collision conditions. Rate constants were also measured for electronic quenching of CN(B 2Σ+,v=0,Ni=4,7,8,and 11) by H2. In general, state-to-state RET rate constants showed very small or no even–odd alternations as the final rotational state varied. Total rate constants for CN(X 2Σ+,v=2,N)/H2, D2 were found to decrease with increasing rotational quantum number, N. By contrast, total rate constants for CN(B 2Σ+,v=0,N)/H2 were found to be relatively independent of N. Exponential energy gap and angular momentum fitting functions were found to represent measured state-to-state RET rate constants very well and were substantially equally effective in this regard. © 2002 American Institute of Physics.

Notes: Families of model "rugged landscape" potential energy functions have been constructed and examined, in order to clarify the molecular-level basis for the relationship between thermodynamic and kinetic behaviors of glassforming substances. The general approach starts by forming elementary basin units, each of which contains a single local minimum (inherent structure). These units are then spliced together to create a continuous composite potential with the requisite number of basins, upper and lower limits, and boundary conditions. We demonstrate by example that this approach creates wide topographic diversity. Specifically, many pairs of model potential functions exist that share identical thermodynamic properties (depth distribution of minima), but drastically different kinetics (overall topography). Thus, within the confines of this purely mathematical exercise, the "strong" versus "fragile" classifications of thermodynamics and of kinetics are logically disconnected. We conclude that the empirically-observed correlation between thermodynamic and kinetic behaviors embodied, for example, in the Adam–Gibbs equation, must rest upon an additional physical principle involving details of interparticle interactions, transcending the purely mathematical aspects of potential energy landscape topography. © 2002 American Institute of Physics.

Notes: Soret coefficients and mass diffusion coefficients of three states of the n-pentane–n-decane mixture have been measured by thermal diffusion forced Rayleigh scattering (TDFRS) and are compared with molecular dynamics simulations values. Both equilibrium (EMD), synthetic (S-NEMD), and boundary driven (BD-NEMD) nonequilibrium techniques have been applied to compute the phenomenological and the transport coefficients relevant to the Soret effect. It is found that statistical error on cross-coefficients using equilibrium and dynamical S-NEMD is too high to enable any comparison with experiments, whereas stationary S-NEMD and BD-NEMD methods have statistical error less than (approximate)35%. S-NEMD simulations have been carried out in the center-of-mass reference frame and the resulting transport coefficients transformed to the center-of-volume frame of reference. The mass diffusion coefficients are sensibly affected by this transformation and show the same weight fraction dependence as the experimental value, although a difference of roughly a factor of 1.4 is found. The Soret coefficients are, as expected, unaffected by the frame of reference transformation and a good agreement between experiment and simulations is found. © 2002 American Institute of Physics.

Notes: The microscopic interactions and dynamics probed by third-order Raman spectroscopy in an atomic liquid (Xe) are explored within the Drude oscillator model, both numerically and analytically. Many-body polarization effects reduce the coefficient of the effective dipole–induced-dipole tensor. The isotropic part of the effective dipole–induced-dipole tensor arises primarily from the three-body interaction and is short-ranged. With an isotropic sample, the Raman response in any polarization geometry can be rigorously decomposed into an isotropic component and an anisotropic component, which primarily measure the strength and evolution of the two-body and three-body interactions, respectively. An interesting result from our analysis is the derivation of the standard mode-coupling equation for the intermediate scattering function and the mode-coupling equation for the bilinear density mode using Gaussian factorization of the memory kernel and the mean spherical approximation of the direct correlation function. The initial moment expansion along with the Gaussian factorization scheme allows us to predict the temporal profile of the Raman response function with reasonable accuracy. Furthermore, the Kirkwood superposition scheme approximates the Raman correlation function with pair distribution functions and time correlation functions and allows us to predict the ratio of the pair, three-particle, and four-particle contributions. These results, though obtained for Xe, are generally helpful in interpreting third-order spectroscopies of other liquids. © 2002 American Institute of Physics.

Notes: The adsorption of 1,4-cyclohexadiene on the Si(001) surface is studied by first-principles density-functional calculations within the generalized gradient approximation. The "pedestal" structure where the two C(Double Bond)C double bonds react with different Si dimers is found to be more stable than the "upright" structure where only one of the two C(Double Bond)C bonds reacts with a Si dimer. However, the [2+2] cycloaddition reaction can easily form the upright structure but not the pedestal one. The latter structure can be obtained from the former through a high energy barrier of ∼0.95 eV, indicating a small reaction rate at room temperature. Our results provide the theoretical basis for the interpretation of recent low-energy electron diffraction and photoelectron spectroscopy data in which the upright structure was seen. © 2002 American Institute of Physics.

Notes: We have studied metallic and oxidized chromium layers on thin ordered alumina films grown on a NiAl(110) substrate using x-ray photoelectron spectroscopy. The interaction between the chromium layers and the substrate has been characterized after deposition at room temperature and after oxidation at 300 and 700 K. Our results indicate partial oxidation of the deposited chromium with the fraction of oxidized Cr decreasing with increasing Cr coverage. Oxidation of the chromium layers at room temperature using O2 results in Cr3+ species on the surface. These oxidized chromium species can be reduced by heating the sample to 700 K for 5 minutes. Oxidation at 700 K results in chromium species that cannot be thermally reduced. Our results do not indicate formation of Cr6+ species although such are present in impregnated catalysts. © 2002 American Institute of Physics.

Notes: The effects of intrinsic fluctuations on bistable dynamics of a chemical system are investigated within the framework of a chemical master equation. Calculations are carried out for a three-variable mesoscopic model of the chemical Chua reaction, a mass-action model that displays the bistable state consisting of a period-1 and chaotic states. Contrary to the deterministic description, the chaotic state can be stable or unstable strongly depending on the system size, indicating a new concept of stability concerning multistable states in mesoscopic dynamics. In addition, the intensity of intrinsic fluctuations for one variable of the system is quite larger than those for the other two variables, implying that the data information obtained by measuring one variable in experiments may not reconstruct the real dynamic behavior of the system. Their implications for ecological and microscopic biological systems are also pointed out. © 2002 American Institute of Physics.

Notes: Accurate quantum mechanical results for the thermal rate constant of the prototypical six atom reaction, CH4+H→CH3+H2, are reported in this article. Previous k(T) results for temperature values below 500 K are extended up to 1000 K. This is achieved employing a combined iterative diagonalization and statistical sampling approach for the evaluation of the flux correlation function. The accurate reaction rate data obtained for the extended temperature range is used to test several approximations related to the transition state theory. The study especially focuses on the contribution of vibrationally excited states of the activated complex to the thermal rate constant. © 2002 American Institute of Physics.

Notes: Trajectory surface hopping calculations have been carried out for collisions of Ar++H2 (v=0), Ar++HD (v=0), H2+(v)+Ar, and HD+(v)+Ar, where v=0, 1, and 2 on the Kuntz–Roach diatomics-in-molecules potential surfaces at a relative energy of 0.1 eV. The importance of the mutual "capture" of the two particles on the attractive ground potential energy surface is shown clearly. The fact that capture does not occur on every collision is attributed to an effect of the vibrational phase of the H2 or HD molecule. This vibrational phase effect can explain the drop in the experimental rate constant seen at very low temperatures in the Ar++H2 system. For H2+(v=2)+Ar and HD+(v=2)+Ar we also find that many trajectories hop to the first excited potential surface as the particles approach. Since these trajectories cannot reach small separations, this further reduces the reactive cross section for v=2 and higher levels. The ground potential energy surface has a fairly deep well, particularly when the Ar–H–H angle is near 90°. Hence, once capture occurs in the (Ar–H–D)+ system, the Ar–H and Ar–D distances rapidly interchange. The product ArD+ is always favored over ArH+ because the H atom can more easily escape the complex. Finally, the reactivity of Ar++H2 (v=0) is seen to be intermediate between that of H2+ (v=1) and H2+ (v=2) with Ar. © 2002 American Institute of Physics.

Notes: The Raman spectra of P4 and P2 molecules have been studied in nitrogen, argon, krypton, and xenon matrices at 15 K. The vibrational frequencies of the P4 molecule are up to 14 cm−1 higher than the experimental gas phase data. This apparent blue-shift is not caused by matrix effects but rather due to an underestimation of the fundamentals in the gas phase as a course of the elevated temperatures. The observed frequencies confirm a recent theoretical prediction on the basis of high-level calculations. From the observed frequencies of the P4 molecule a general valence force field was calculated. © 2002 American Institute of Physics.

Notes: The prediction of viscosity by molecular simulation has been a goal of molecular modeling essentially since its inception. With today's computing power, the Newtonian or zero shear viscosity of a low molecular weight fluid can easily be determined using equilibrium and nonequilibrium molecular dynamics simulation methods. However, both methods are constrained to systems with relatively short relaxation times that are accessible on the timescale of a molecular dynamics simulation. Here we demonstrate that using a simple scaling relation enables us to predict the Newtonian viscosity of a molecule at any state point for a small fraction of the time that it takes to obtain the same result through nonequilibrium or equilibrium molecular dynamics simulation. © 2002 American Institute of Physics.

Notes: The reverse nonequilibrium molecular dynamics [F. Müller-Plathe, Phys. Rev. E 49, 359 (1999)] presented for the calculation of the shear viscosity of Lennard-Jones liquids has been extended to atomistic models of molecular liquids. The method is improved to overcome the problems due to the detailed molecular models. The new technique is besides a test with a Lennard-Jones fluid, applied on different realistic systems: liquid nitrogen, water, and hexane, in order to cover a large range of interactions and systems/architectures. We show that all the advantages of the method itemized previously are still valid, and that it has a very good efficiency and accuracy making it very competitive. © 2002 American Institute of Physics.

Notes: Time-resolved transient grating experiments with various polarizations are used to separate different responses and measure their dynamics in supercooled liquid salol. A contribution to signal from orientational alignment induced by flow that arises from thermal expansion is demonstrated. This contribution is distinct from that due to orientational alignment induced directly by the excitation light through the molecular polarizability anisotropy (i.e., through the optical Kerr effect). It is also distinct from signal contributions due to density modulations induced by thermal expansion. The results offer additional insight into salol dynamics and into time-dependent transient grating measurements of this class. Depending on the light polarizations used, any of the signal contributions can be eliminated or highlighted. © 2002 American Institute of Physics.

Notes: The crystal-melt interfaces of a binary hard-sphere fluid mixture in coexistence with a single-component hard-sphere crystal is investigated using molecular-dynamics simulation. In the system under study, the fluid phase consists of a two-component mixture of hard spheres of differing size, with a size ratio α=0.414. At low pressures this fluid coexists with a pure fcc crystal of the larger particles in which the small particles are immiscible. For two interfacial orientations, [100] and [111], the structure and dynamics within the interfacial region is studied and compared with previous simulations on single component hard-sphere interfaces. Among a variety of novel properties, it is observed that as the interface is traversed from fluid to crystal the diffusion constant of the larger particle vanishes before that of the small particle, defining a region of the interface where the large particles are frozen in their crystal lattice, but the small particles exhibit significant mobility. This behavior was not seen in previous binary hard-sphere interface simulations with less asymmetric diameters. © 2002 American Institute of Physics.

Notes: Intrachain exciton quenching in ladder-type polyparaphenylene has been quantified for the first time. Two-phonon absorption and subsequent upconverted photoluminescence of ladder-type polyparaphenylene and polyfluorene has been measured and analyzed with a new theoretical framework for the two-photon absorption saturation. This microscopic analysis determines the number of singlet excitons as a function of the excitation intensity, which is compared to the photoluminescence intensity. The absorption saturation alone perfectly describes the photoluminescence saturation in polyfluorene, whereas in ladder-type polyparaphenylene, exciton–exciton quenching occurs. By measuring in solution, the formation of stacked polymer chains is prevented. Therefore, the quenching is due to intrachain interaction. © 2002 American Institute of Physics.

Notes: We investigate vapor–liquid equilibria of dendrimer/solvent (benzyl ether dendrimer/toluene) systems by the combination of incompressible lattice cluster theory and atomistic simulation technique. We also examine the structure effect of dendritic polymer and the specific interaction due to the difference of interaction energies of endgroup at the periphery of dendrimer molecules. The interaction energy parameters are obtained by the pairs method including Monte Carlo simulation technique with excluded volume constraint. In the pairs method, we do not simulate the whole molecule as in molecular dynamics or molecular mechanics, but only monomer segments interacting with solvent molecules. In general, those parameters are determined by fitting experimental data. Our results show that the specific interactions between the endgroup and the solvent molecule play an important role in determining phase behaviors of the given systems. © 2002 American Institute of Physics.

Notes: We have determined the diffusion constants of oxygen molecule (DO2) in near- and supercritical water (the SPCE model) over the wide density region by molecular dynamics simulations. Anomalous temperature dependence of DO2 has been observed: DO2 decreases with increasing temperature from 647 to 773 K at the 115 and 217 kg m−3. The memory function for the friction on the diffusion shows that DO2 is mainly dominated by the binary part of the friction, which is closely related to the contact value of the radical distribution function between oxygen and water. This value decreases with decreasing the temperature from 773 to 647 K, which is a main reason of the peculiar temperature dependence of DO2. © 2002 American Institute of Physics.

Notes: We give a lower bound on the diffusion coefficient of a polymer chain in an entanglement network with kinematic disorder, which is obtained from an exact calculation in a modified Rubinstein–Duke lattice gas model with periodic boundary conditions. In the limit of infinite chain length we show the diffusive motion of the polymer to be slowed down by kinematic disorder by the same factor as for a single particle in a random barrier model. © 2002 American Institute of Physics.

Notes: Fourth-order quantum master equations (FQMEs) are derived in both time nonlocal and local forms for a general system Hamiltonian, with new detailed expressions for the fourth-order kernel, where the bath correlation functions are explicitly decoupled from the system superoperators. Further simplifications can be made for the model of linearly coupled harmonic oscillator bath. Consideration of the high temperature Ohmic bath limit leads to a general Markovian FQME with compact forms of time independent superoperators. Two examples of this equation are then considered. For the system of a quantum particle in a continuous potential field, the equation reduces to a known form of the quantum Fokker–Planck equation, except for a fourth-order potential renormalization term that can be neglected only in the weak system-bath interaction regime. For a two-level system with off-diagonal coupling to the bath, fourth-order corrections do not alter the relaxation characteristics of the second-order equation and introduce additional coherence terms in the equations for the off-diagonal elements. © 2002 American Institute of Physics.

Notes: Kinetic properties of the single rotational states 2≤N≤8 of the electronically excited CH(A2Δ,v=0) radical have been studied in the gas phase at room temperature in the presence of CO. Rate constants of the state-to-state relaxation are presented. Further, rate constants were determined for the electronic quenching of single N states and compared with data recently reported by Cerezo and Martin [J. Photochem. Photobiol., A 134, 127 (2000)]. The radiative lifetimes of the rotational levels are given, too. © 2002 American Institute of Physics.

Notes: It is shown that the accuracy of quantum dynamics calculations obtained according to the Herman–Kluk (HK) semiclassical initial value representation (SC-IVR) is significantly improved when the time evolution operator is computed by concatenating finite time propagators. This approach results in an approximate calculation of a real-time path-integral in a discrete coherent-state representation, which becomes exact in the limit of sufficiently short time-slice intervals. The efficiency of the computational method is optimized by devising a compact coherent-state basis set that obviates the need for calculating the inverse overlap matrix. Quantitative agreement with full quantum mechanical results is verified in the description of tunneling between disjoint classically allowed regions in one- and two-dimensional systems, in the treatment of long-time dynamics, and in nonadiabatic dynamics in a model system with two coupled one-dimensional potential energy surfaces. © 2002 American Institute of Physics.

Notes: Minimal Electron Nuclear Dynamics theory is applied to D2+NH3+ reaction at collision energies from 6 to 16 eV in the center-of-mass frame. This method for direct nonadiabatic dynamics describes the electrons with a family of complex determinantal wave functions in terms of nonorthogonal spin orbitals and treats the nuclei as classical particles. There are no geometrical constraints imposed on this six-atom system. Emphasis is put on the details of the abstraction and exchange reaction mechanisms for ground-state reactants. Comparisons are made to recent molecular-beam experiments. © 2002 American Institute of Physics.

Notes: Solving integral equations is an effective approach to obtain the radial distribution function (RDF) of multicomponent mixtures. In this work, by extending Gillan's approach [M. J. Gillan, Mol. Phys. 38(6), 1781 (1979)], the integral equation was solved by numerical method and was applied to both binary and ternary mixtures. The Lennard-Jones (LJ) potential function was used to express the pair molecular interactions in calculating the RDF and chemical potential. This allowed a comparison with available simulation data, on the RDF and the chemical potential, since the simulation data have been reported for the LJ potential function. The RDF and the chemical potential results indicated good agreement with the simulation data. The calculations were extended to the ternary system and the RDFs for carbon dioxide–octane–naphthalene were obtained. The numerical method used in solving integral equation was rapidly convergent and not sensitive to the first estimation. The method proposed in this work can be easily extended to more than the three-component systems. © 2002 American Institute of Physics.

Notes: In this paper, we present an analysis of condensed phase chemical reactions from the perspective of qualitative dynamical systems theory. Our approach is based on a phenomenological phase space representation of the generalized Langevin equation (GLE). In general, the GLE with memory requires an infinite-dimensional phase space for its description. The phenomenological phase space is constructed by augmenting the physical phase plane (q,p) with additional variables defined as the convolution of the system momentum with the memory kernel and its time derivatives. The qualitative dynamics in this representation are then characterized in terms of the eigenvalues and eigenvectors of the linear system near the barrier top. The phase space decomposes into a single unstable direction and a complementary stable subspace. The rate of exponential growth along the unstable eigenvector is directly related to the rate of chemical reaction, and our linear analysis reproduces the Grote–Hynes expression for the reaction rate [R. F. Grote and J. T. Hynes, J. Chem. Phys. 73, 2715 (1980)]. In the presence of noise, the stable subspace can be identified with the stochastic separatrix, a manifold of initial conditions with a reaction probability of 0.5. Other dynamical processes, such as solvent caging, can also be given a simple geometric interpretation in terms of the qualitative dynamical analysis. © 2002 American Institute of Physics.

Notes: When radiation is scattered by a medium, a part of its momentum is transferred to the target particles. This is purely a mechanical force which comes into effect when radiation is not coherently interacting. This force is known in literature as radiation pressure. Recent experimental studies have demonstrated the feasibility of using radiation pressure of a laser beam as a tool for cluster formation in solution. In this paper we describe the Brownian dynamics simulation of solute molecules under the perturbation induced by laser radiation. Here the force field generated by a laser beam in the fundamental mode is modeled as that of a two-dimensional harmonic oscillator. The radial distribution function of the perturbed system gives indication of high inhomogeneities in the solute distribution. An explicit analysis of the nature of these clusters is carried out by calculating the density–density correlation functions in the plane perpendicular to beam direction g(rxy); and along the direction of beam g(z), they give an average picture of shell structure formation in the different directions. The relaxation time of the first shell structure calculated from the van Hove correlation function is found to be relatively large in the perturbed solution. This is the signature of formation of stable nanoclusters in the presence of the radiation field. Our study on the dynamics of solute molecules during the cluster formation and dissolution gives the duration of collective relaxation, far away from the equilibrium to an equilibrium distribution. This relaxation time is found to be large for a perturbed solution. © 2002 American Institute of Physics.

Notes: A continuum elastic model of fullerenes is presented by utilizing the analogy between the closed carbon cages and elastic shells. We derive expressions for the curvature related strain energies Ep of the pentagonal protrusions. We propose to explain the observed sphericity of the carbon onions shells as opposed to the predicted protrusions around the pentagonal defects on the basis of our continuum elastic model of fullerenes. In our model the energy inherent in the pentagonal protrusions Ep is due to the stretching and bending of the shell and shown to be a function of the structural parameters. It also defines the upper limit on the size of the free-standing fullerenes. Using Ep and the topological arguments, we show that the pentagonal protrusions will be smoothed out, resulting in spherical shells of the carbon onions denoted as C60@C240@C540@C960@C1500,... . © 2002 American Institute of Physics.

Notes: Vibronic interaction and its role in the occurrence of possible superconductivity in the monoanions of phenanthrene-edge-type aromatic hydrocarbons are studied. The vibrational frequencies and the vibronic coupling constants are computed and analyzed and the electron–phonon coupling constants are estimated. The results for phenanthrene-edge-type hydrocarbons are compared with those for acene-edge-type hydrocarbons. The lowest frequency mode and the C–C stretching modes of 1400–1600 cm−1 afford large electron–phonon coupling constants in the monoanions of acene- and phenanthrene-edge-type hydrocarbons. The total electron–phonon coupling constants decrease with an increase in the number of carbon atoms in both acene- and phenanthrene-edge-type hydrocarbons, but those for the monoanions of phenanthrene-edge-type hydrocarbons are larger than those for the monoanions of acene-edge-type hydrocarbons. Possible superconducting transition temperatures Tcs for the monoanions are estimated. The monoanions of phenanthrene-edge-type hydrocarbons would have higher Tcs than the monoanions of acene-edge- type hydrocarbons if phenanthrene-edge-type hydrocarbons exhibit superconductivity. These results suggest that molecular edge structures as well as molecular sizes have relevance to the strength of electron–phonon coupling and Tcs. The fragment molecular-orbital method (FMO) method successfully characterizes the distinct electronic structures of the two small polynuclear aromatic hydrocarbons (PAHs) with different type of edges such as anthracene and phenanthrene. © 2002 American Institute of Physics.

Notes: In this paper, we present a systematic Monte Carlo study of the self-assembly of nonionic, amphiphilic, chainlike molecules in dilute solution. The focus is on the regime in which the molecules form relatively weakly segregated micelles, which are in equilibrium with small submicellar aggregates. We study the size and shape distributions of the aggregates, and the structure of the aggregates' cores and surfaces. In some cases, spherical micelles, relatively large nonspherical micelles, and submicellar aggregates, all coexist. The size distributions of the spherical micelles are approximately Gaussian, while the nonspherical micelles contribute non-Gaussian tails at relatively large aggregation numbers. The simulation results are interpreted in terms of a simple theory of spherical micelles, and the size distributions are compared with its predictions. For the cases where the agreement is good, we combine the simulations and the theory to calculate the critical micelle concentration as functions of the chain lengths and solvent quality. In cases where there are nonspherical aggregates, the asphericity is quantified using the principal radii of gyration of the micelles, and the size distributions are compared with mean field predictions that account for both spherical and nonspherical aggregates. © 2002 American Institute of Physics.

Notes: A new Monte Carlo move for polymer simulations is presented. The "wormhole" move is build out of reptation steps and allows a polymer to reptate through a hole in space; it is able to completely displace a polymer in time N2 (with N the polymer length) even at high density. This move can be used in a similar way as configurational bias; in particular, it allows grand canonical moves, it is applicable to copolymers, and can be extended to branched polymers. The main advantage is speed, since it is exponentially faster in N than configurational bias, but is also easier to program. © 2002 American Institute of Physics.

Notes: The dynamical behavior and equilibrium distribution of linear bead-rod and bead-spring polymers differ even in the limit of infinitely stiff springs. Imposing metric pseudopotential forces on the bead-rod chains yields the behavior of bead-spring chains in Langevin and Brownian Dynamics simulations. Here we present a simple, compact, and efficient algorithm for computing the required metric correction forces at minimal computational cost. © 2002 American Institute of Physics.

Notes: In a previous paper of this series [Paper III: Nakatsuji, J. Chem. Phys. 105, 2465 (2001)], the author showed a high potentiality of the extended coupled cluster (ECC) method to calculate the exact wave function of the ground state. In this paper, we propose ECC-configuration interaction (CI) method, which is an accurate useful method to calculate the excited states from the ECC wave function of the ground state. In contrast to the ECC method, the standard ECC-CI method is approximate, but we can make it exact by generalizing its excitation operator (ECC-CI general). The ECC-CI method is applicable not only to the excited states having the same spin-space symmetry as the ground state, but also to those having different spin-space symmetries and to the ionized and electron-attached states. The theoretical framework of the ECC-CI method is similar to that of the symmetry-adapted-cluster (SAC)-CI method proposed in 1978 by the present author. Next in this paper, we examine the performance of the methods proposed in this series of papers for a simple one-dimensional harmonic oscillator. The iterative configuration interaction (ICI) and ECC methods are examined for the ground state and the ICI-CI and ECC-CI methods for the excited states. The ICI method converges well to the exact ground state and the excited states are calculated nicely by the ICI-CI method in both the standard and general active spaces. In contrast to the simplest (S)ECC examined in Paper III, the ECC2 method shows quite a rapid convergence to the exact ground state, which enables us to calculate the true exact wave function in the ECC form. The ECC-CI methods in both the standard and general active spaces also work well to calculate the excited states. Thus, we conclude that the ICI and ECC approaches have a potentiality to provide useful method to calculate accurate wave functions of the ground and excited states. A merit of ECC is that it provides the exact wave function in a simple explicit form. © 2002 American Institute of Physics.

Notes: Accurate estimates of the magnetic coupling in binuclear complexes can be obtained from ab initio configuration interaction (CI) calculations using the difference dedicated CI technique. The present paper shows that the same technique also provides a way to analyze the various physical contributions to the coupling and performs numerical analysis of their respective roles on four binuclear complexes of Cu (d9) ions. The bare valence-only description (including direct and kinetic exchange) does not result in meaningful values. The spin-polarization phenomenon cannot be neglected, its sign and amplitude depend on the system. The two leading dynamical correlation effects have an antiferromagnetic character. The first one goes through the dynamical polarization of the environment in the ionic valence bond forms (i.e., the M+(centered ellipsis)M− structures). The second one is due to the double excitations involving simultaneously single excitations between the bridging ligand and the magnetic orbitals and single excitations of the environment. This dispersive effect results in an increase of the effective hopping integral between the magnetic orbitals. Moreover, it is demonstrated to be responsible for the previously observed larger metal-ligand delocalization occurring in natural orbitals with respect to the Hartree–Fock ones. © 2002 American Institute of Physics.

Notes: The photoionization dynamics of rotationally hot CO, photodissociated from OCS, have been studied using laser photoelectron spectroscopy via the intermediate B 1Σ+ Rydberg state leading to the X 2Σ+ of the ion. The photodissociation of OCS near 230 nm produces rotationally hot, but vibrationally cold CO (X 1Σ+,N″,v″=0,1) fragments along with S (1D) atoms. These high rotational levels show photoelectron spectra with a very strong ΔN=0 transition and weaker ΔN=±1, ±2, and ±3 transitions. Agreement between measured and calculated spectra is good and suggests that there is significant angular momentum coupling in the photoelectron orbital. In the ionization step not only Δv=0, but also off-diagonal, non-Franck–Condon (Δv≠0) transitions are observed. The intensities of these transitions vary strongly within the region studied and can be explained by the excitation of superexcited Rydberg states with an A 2Π core. © 2002 American Institute of Physics.

Notes: The primary photodissociation dynamics of allyl chloride upon excitation at 193 nm is investigated in a crossed laser-molecular beam scattering apparatus. Tunable vacuum ultraviolet (VUV) photoionization of the products provides a unique ability to learn about the secondary reaction products of the nascent photoproducts formed. The data show evidence for four significant primary reaction channels: a previously unidentified low kinetic energy C–Cl bond fission channel producing unstable allyl radicals, an excited state C–Cl bond fission channel producing Cl atoms with high translational energy, an HCl elimination pathway releasing significant energy to product translation to HCl and its momentum-matched mass 40 partner, and an HCl elimination channel producing low kinetic energy HCl products and predominantly unstable mass 40 products. The measured branching of these primary reaction channels of [all C–Cl] : [fast C–Cl] : [slow C–Cl] : [fast HCl] : [slow HCl] : [all HCl] is 1.00: 0.971: 0.029: 0.291: 0.167: 0.458 (where fast refers to the high recoil kinetic energy channels). The high internal energy allyl radicals formed in the slow C–Cl fission pathway of allyl chloride further dissociate/isomerize, as do the unstable mass 40 products formed in the HCl elimination pathways, and these products are investigated. Photoionization efficiency (PIE) curves of the HCl product suggest that a three-centered elimination mechanism contributes significantly to an observed HCl elimination reaction. © 2002 American Institute of Physics.

Notes: We have performed the first ab initio computational investigation of the elastic scattering of electrons by the isolated cluster which was described with its symmetry lowered (due to Jahn–Teller distortion) to the C2 and Ci point groups. The energy range considered was 1–10 eV. The geometry and electronic energy of the molecule were taken to be those of its ground state. The total and partial cross sections were calculated through a coupled-channel dynamics with inclusion of a parameter-free model exchange and correlation-polarization potentials. The scattering process has been found to exhibit a rather complex resonant structure due to the special "hollow" framework of the molecular cage. One distinguishing feature of the cross sections is the presence of strong near-threshold peaks which we attribute to a series of C20− metastable negative ions. The present results therefore provide a benchmark calculation which could be of guidance to future experiments on the very recently produced fullerene C20 species. In fact, the analysis carried out in the present work allows us to assign each scattering resonance to a specific molecular state, their symmetries and parameters obtained from our calculations. © 2002 American Institute of Physics.

Notes: When the spin–orbit interaction is included, the character of a conical intersection in a molecule with an odd number of electrons differs dramatically from that of its nonrelativistic counterpart. In contrast to the two-dimensional branching space (η=2) in the nonrelativistic case, for these conical intersections the branching space is five-dimensional (η=5) in general, or three-dimensional (η=3) when Cs symmetry is present. Recently we have introduced an algorithm, based on analytic gradient techniques, to locate such conical intersections and used related techniques to efficiently construct and study the properties of the vectors defining the branching space. Here we extend this analysis. A perturbative description of the η=3 case is reported and used to determine the energy, derivative couplings, and a "rigorous" diabatic basis in the vicinity of a conical intersection. The perturbative results are compared with those of exact numerical calculations employing model Hamiltonians. The implications for the nuclear motion problem are discussed. © 2002 American Institute of Physics.

Notes: It is known that SO42− is not electronically stable as an isolated species but can be rendered stable by solvation (e.g., by adding a few H2O molecules). Recently, our group introduced a Coulomb repulsion model that offers an approximation to the energy instability and lifetimes of such species. In order to achieve an independent and likely more reliable estimate of the instability of SO42−, we have undertaken a follow-up study of this dianion. Specifically, we apply a stabilization method to determine the vertical electronic energy difference between the metastable SO42− dianion and its SO4−1 daughter at several levels of theory. The particular variant of the stabilization method used here involves adding a partial positive charge to the central sulfur nucleus in order to confine the escaping electron. Our coupled-cluster data, which represent our highest level of theory, suggest that SO42− is unstable by 1.1 eV and has a lifetime with respect to electron loss of 1.6×10−10 s (our earlier estimates were 0.75 eV and 2.7×10−8 s). © 2002 American Institute of Physics.

Notes: An ab initio adiabatic and diabatic study of the KH molecule is performed for all states below the ionic limit [i.e., K (4s, 4p, 5s, 3d, 5p, 4d, 6s, and 4f)+H(1s)] in 1Σ+ and 3Σ+ symmetries. Adiabatic results are also reported for 1Π, 3Π, 1Δ, and 3Δ symmetries. The ab initio calculations rely on pseudopotential, operatorial core valence correlation, and full valence CI approaches, combined to an efficient diabatization procedure. For the low-lying states, our vibrational level spacings and spectroscopic constants are in very good agreement with the available experimental data. Diabatic potentials and dipoles moments are analyzed, revealing the strong imprint of the ionic state in the 1Σ+ adiabatic states while improving the results. The undulations of the diabatic curves and of the triplet–singlet diabatic energy difference which we found positive, as in Hund's rule, are related to the Rydberg functions. As for LiH, the vibrational spacing of the A state is bracketed by our results with and without the improvement taking into account the diabatic representation. Experimental suggestions are also given. © 2002 American Institute of Physics.

Notes: Homogeneous nucleation of a new phase near an Ising-type critical point of another phase transition is studied. A scaling analysis shows that the free energy barrier to nucleation contains a singular term with the same scaling as the order parameter associated with the critical point. The total magnetization of the nucleus scales as the response function and so it diverges. Vapor–liquid critical points are in the Ising universality class and so our results imply that near such a critical point the number of molecules in a nucleus of another phase, such as a crystalline phase, diverges as the isothermal compressibility. The case where symmetry prevents coupling between the nucleus and the order parameter is also considered. © 2002 American Institute of Physics.

Notes: Acoustical absorption spectra between 10 kHz and 2 GHz are reported for various monosaccharides in water. With the exception of solutions of methyl-β-D-arabinopyranoside (0.5 mol/l) the spectra reveal absorption with relaxation characteristics in excess to the asymptotic high frequency absorption term. Up to three relaxation terms per spectrum emerge within the measuring frequency range. Regression analysis of the measured spectra in terms of a suitable analytical spectral function yields five relaxation regimes with relaxation times on the order of 1 μs, 100 ns, 10 ns, 1 ns, or 100 ps, respectively. These relaxation regimes are assigned to the chair–chair ring inversion, two modes of pseudorotation, an exocyclic side group isomerization and a molecular association mechanism. Particular emphasis is given to the ring inversion which is additionally verified by time resolved measurements of nonequilibrium tautomer systems, utilizing the coupling of the inversion to the carbohydrate mutarotation. Further evidence is derived from measurements of solutions of D-fructose in mixtures of ethanol and water. © 2002 American Institute of Physics.

Notes: In this article we describe a novel, phenomenologically based computer simulation approach for studying relaxation dynamics in fluid systems. The method utilizes an ensemble consisting of two isothermal chambers initially separated by an impermeable partition. The fluid configurations in each chamber are initially pre-equilibrated at densities ρ¯+cursive-epsilon and ρ¯−cursive-epsilon respectively, where ρ¯ reflects an average density of interest and cursive-epsilon a small perturbation about this value. After the pre-equilibration step the partition is removed and the entire ensemble allowed to relax towards an equilibrium state guided by a kinetic Monte Carlo computer simulation algorithm. Fickian transport coefficients are found from quantities calculated during this relaxation process. We present an analysis of the approach and illustrate its application to transport property calculations in purely diffusive lattice-gas systems. Our results focus upon the critical region for which there are few published results and where simulation results face the most challenges because of finite-size effects and the phenomenon known as critical slowing-down. © 2002 American Institute of Physics.

Notes: Dissociative adsorption of O2 on Cu(001)-(2(square root of 2)×(square root of 2))-O was shown to induce Cu2O epitaxial islands on the surface. The initial dissociative sticking probability of O2 on Cu(001)-(2(square root of 2)×(square root of 2))-O scaled with the total translational energy of incident O2, suggesting that the interaction potential was highly corrugated. The sticking probability decreased with increasing translational energy of incidence and increased with increasing surface temperature. For lower translational energy of incident O2 (≤130 meV), the velocity distribution of the scattered molecules was of nonshifted Maxwellian-type, indicating trapping desorption. The translational temperature of the trapping desorption was lower than the surface temperature and increased linearly with surface temperature, suggesting that there was no barrier for desorption. Neither thermal desorption experiments nor velocity distribution analysis of the trapping desorption showed any evidences of recombination desorption. These results were interpreted as an activated dissociation via a trapping precursor. The activation barrier for dissociation was estimated as 330 meV. The angular distribution of the trapping desorption was fitted well by cos2 θ, which was in contrast to the expectation of a cosine angular distribution based on the detailed balance arguments. The discrepancy may have been attributable to preferential consumption of the parallel momentum of the trapped O2 for dissociation and imbalance between adsorbing and desorbing O2 flux. © 2002 American Institute of Physics.

Notes: We propose a self-consistent mean-field lattice-gas theory of intercalation compounds based on effective interactions between interstitials in the presence of the host atoms. In addition to short-range screened Coulomb repulsions, usually discussed in the lattice gas models, the present theory takes into account long-range effective attractions between intercalants due to elasticity of the host matrix. The mean-field phase diagram in the space of interaction parameters contains the domains of first- and second-order transitions of the order-disorder type, separated by a tricritical line, and the domain of the first-order transition of the gas–liquid-type separated from the homogeneous state by a critical line. Theoretical predictions are shown to be in qualitative agreement with the grand canonical Monte Carlo simulations. The peculiarities of the phase diagram give an insight into different types of behavior of the open circuit voltage observed in rechargeable batteries, in which an intercalation compound is used as an electrode material. © 2002 American Institute of Physics.

Notes: Confinement of phantom networks of Gaussian chains between parallel surfaces is simulated through the application of a harmonic potential 〈fraction SHAPE="CASE"〉12Hx2 to each chain bead at a distance x from the mean plane. We consider infinite, square (cubic) networks with a topological dimensionality of two (three), in addition to three-dimensional networks with a finite number of layers along one dimension. The partition function stays Gaussian and its integration reduces to the search of the eigenvalues of cyclic, or quasicyclic matrices. As applied to an isolated chain the confinement energy is 75% the exact value obtained by Casassa's exact approach, and the accuracy is expected to improve in the network case. At strong compressions, the confinement energy per chain EH is about the same for all the networks, but smaller than for a single chain with the same contour length. Taking EH in kBT units, M=EH−1 gives the number of chains in the correlation domain. Therefore, the external potential breaks up the network into smaller and smaller correlated domains, whose statistics remain unperturbed ("blobs"). The unperturbed mean-square radius of gyration reproduces previous results on the two- and the three-dimensional networks. The enormous collapse in the three-dimensional case is evidenced once again. © 2002 American Institute of Physics.

Notes: We have developed a simulation technique, based on a dynamic mean field theory to describe the evolution of a melt of liquid crystalline polymers that is quenched below its isotropic–nematic transition temperature. The polymers are described by chains characterized by a bending energy depending on the angles between consecutive chain segments and a Maier Saupe term accounting for the effect of mutual alignment of the segments in the melt. The equations for the time evolution of the system depend on coarsened variables, which are the density ρ(r) and the orientation distribution S(underbar)(r). The density field ρ evolves according to a diffusion-type equation, whereas the orientation field S(underbar) follows a growth equation. © 2002 American Institute of Physics.

Notes: We present a theory for describing nonclassical dynamics of reactions occurring in disordered media based on the fractional diffusion equation. An exact expression is derived for the Green's function required to calculate the survival probabilities of reactants. A novel temperature-dependent kinetic phase transition is found: The exponent γ in the asymptotic power-law decay (∝t−γ) of the geminate survival probability increases with temperature T below a critical temperature T*, but decreases with T above T*. The present theory explains in a unified manner the observed features of ligand-protein recombination reactions for a wide range of temperature and time scales. © 2002 American Institute of Physics.

Notes: Explicit atom molecular dynamics simulations were used in conjunction with the thermodynamic integration method to calculate hydration free energies for short n-alkane molecules, up to C5H12. The OPLS all-atom parameter set [Kaminski et al., J. Phys. Chem. 98, 13077 (1994)] was used to represent the n-alkanes, together with the TIP3P water model [Jorgensen et al., J. Chem. Phys. 79, 926 (1983)]. The approach of Beutler et al. [Chem. Phys. Lett. 222, 529 (1994)] was used to avoid singularities in nonbonded interaction potentials that can otherwise be problematical with this technique. Electrostatic interactions were treated using a cutoff radius of 0.9 nm, and a functional form that was shifted and scaled smoothly to zero. The values obtained for the solvation free energies were of similar accuracy to those from previously published simulations, but were systematically about 2 kJ mol−1 higher than experimental values. However, the calculated free energies of transformation for the reaction CnH2n+1(aq)→Cn+1H2n+4(aq), show a considerably improved agreement over previous values, and reproduce well the experimental trend versus n. The merits of the thermodynamic integration technique are discussed in relation to the popular thermodynamic perturbation method. © 2002 American Institute of Physics.

Notes: Close-coupling calculations of bound rotational and vibrational states are carried out on a new intermolecular potential energy function based on 200 energies of the He⋅NO+ cationic complex calculated at the coupled-cluster single double (triple)/aug-cc-pV5Z ab initio level of theory at a range of geometries and point-by-point corrected for basis set superposition error. The potential energy function is constructed by combining the reciprocal power reproducing kernel Hilbert space interpolation with Gauss–Legendre quadrature. The best estimate of the intermolecular dissociation energy, De, is 198±4 cm−1, obtained by extrapolations to the complete basis set limit, and calculating estimates for relativistic effects and core and core-valence correlation effects. © 2002 American Institute of Physics.

Notes: We study the local solute–solvent structure in dilute supercritical solutions, using as a model system a dilute Yukawa solute in a supercritical Lennard-Jones fluid. Our primary interest is in the effect of the solute–solvent interaction range on the local solvent density around the solute. We employ the integral equation theory for inhomogeneous fluids to calculate the solute–solvent structural properties. The theory is shown to be in excellent agreement with Monte Carlo simulations and to provide a substantial improvement over the integral equation theory formulated for homogeneous fluids. In particular, it is demonstrated that the homogeneous theory greatly overestimates the local density enhancement for long-ranged solute–solvent interactions in the highly compressible supercritical regime. © 2002 American Institute of Physics.

Notes: This work exploits the passive phase stabilization of diffractive optics to implement heterodyne detection of the complete χ(5) tensor of liquid CS2 as an example of a simple liquid. This approach permits the use of two different colors for the excitation, probe, and detection beam protocols and enables full optimization of the signal with respect to discrimination against lower order cascaded third-order responses. This work extends the previous study of polarization selectivity, in combination with heterodyne detection, to all independent polarization components to provide further insight into the origins of the fifth-order response and its connection to the multitime correlation of the liquid dynamics. The characteristic feature that clearly distinguishes the direct fifth-order response from lower order cascades is the pronounced ridge along the τ4 axis (probe pulse delay) with very rapid decay along the τ2 axis (excitation pulse delay). This observation is in contrast to recent related work using one-color homodyne detection. With the determination of the direct fifth-order and cascaded third-order signal amplitudes made possible by heterodyne detection, this difference can be attributed to cross terms between the direct fifth-order and cascaded third-order terms inherent to homodyne detection under phase matching conditions used to discriminate against cascades. In support of theoretical treatments, the previously predicted enhancement of rephasing pathways for certain polarization components has been observed. However, even for these tensor elements the remarkable feature is the very rapid decay in the nuclear coherence along τ2. The experiment is predicated on the ability of a 2-quantum transition involving the Raman overtone to rephase the nuclear coherence. These findings indicate that the nuclear motions, in the frequency range accessed, are strongly damped and draw into question the validity of the overtone as a viable pathway for rephasing. With the isolation of the direct fifth-order Raman response, new information regarding relaxation and dephasing pathways in liquids can be determined for the highest frequency modes. The results are in very good agreement with a recent finite field molecular dynamics simulation of liquid CS2 with respect to the polarization dependence of signal magnitudes, relative cascade signal amplitudes, and qualitative agreement with respect to the predicted temporal profiles. © 2002 American Institute of Physics.

Notes: The molecular description of friction at a single, ideal microscopic contact of the sort realizable in scanning surface probe devices is greatly complicated by wide variations in the temporal regime t*≡texpt/tr of the measurement, where texpt is the time taken to measure the frictional force Fs and tr is the time required for the system to attain a state of thermodynamic equilibrium. At one extreme (t*(very-much-greater-than)1) the system remains in equilibrium for the duration of the measurement and one can employ statistical thermodynamics (in practice, Monte Carlo simulation) to compute Fs, which depends only on the thermodynamic state. At the other extreme (t*(very-much-less-than)1) the system remains out of equilibrium. One must then account for the dynamic history of the system, typically by means of nonequilibrium molecular dynamics. The range of t* between these extremes can be handled within a single theoretical framework based on the concept of "equivalent equilibrated states." Through addition of auxiliary potential fields to the Hamiltonian specific degrees of freedom of the system can be constrained. The properties of the constrained system are computed from the free energy of the system trapped in the equivalent equilibrated state by the constraints. The constraints are chosen to correspond to t*. The results of the theory applied to a one-dimensional model demonstrate dramatically the impact of history on Fs. © 2002 American Institute of Physics.

Notes: The sequential importance sampling method and its various modifications have been developed intensively and used effectively in diverse research areas ranging from polymer simulation to signal processing and statistical inference. We propose a new variant of the method, sequential importance sampling with pilot-exploration resampling (SISPER), and demonstrate its successful application in folding polypeptide chains described by a two-dimensional hydrophobic-hydrophilic (HP) lattice model. We show by numerical results that SISPER outperformed several existing approaches, e.g., a genetic algorithm, the pruned-enriched Rosenbluth method, and the evolutionary Monte Carlo, in finding the ground folding states of 2D square-lattice HP sequences. In a few difficult cases, the new method can find the ground states without using any prior structural information on the chain. We also discuss the potential applications of SISPER in more general problems. © 2002 American Institute of Physics.

Notes: The vapor pressure, heat of vaporization, and liquid/vapor densities along the coexistence curve of the polarizable water model of Dang and Chang [J. Chem. Phys. 106, 8149 (1997)] were calculated by using Gibbs ensemble Monte Carlo simulation techniques. Long-range interactions such as charge–charge, charge–dipole, and dipole–dipole were evaluated by using Ewald summation techniques. The model yields good agreement with the corresponding experimental data in the lower temperature region, but only moderate agreement in the higher temperature region. The critical temperature and density were estimated to be 565 K and 0.28 g/cm3, compared to experimental Tc=647 K and ρc=0.32 g/cm3. © 2002 American Institute of Physics.

Notes: This article constructs trajectories associated with various boundary conditions for the Smoluchowski equation on an interval. Single-particle diffusion processes are first constructed by taking the diffusion limits of random walks. The diffusion limit gives both boundary conditions which enforce the single-particle constraint and properties of underlying trajectories at those boundaries. Mean-field diffusions are then obtained as limits of sums of single-particle processes. The results help to interpret the application of diffusion models to both ion channels and wider pores that facilitate molecular transport across membranes. Potential applications to Brownian dynamics simulations are discussed. © 2002 American Institute of Physics.

Notes: We investigate on small world networks (SWN's) the survival probability of immobile targets, which get annihilated by random walkers at first encounter. On SWN's we find (distinct from regular lattices, Cayley trees, and regular ultrametric spaces) that in general the survival probability cannot be directly related to the average number of distinct sites visited. We underline this finding with arguments related to the structural disorder of SWN's and through the derivation of a lower bound for the targets' decay. © 2002 American Institute of Physics.

Notes: An improved density matrix functional (DMF) combining the properties of the "corrected Hartree" (CH) and "corrected Hartree–Fock" (CHF) approximations is proposed. Functionals of the CH/CHF type and the closely related natural orbital functional of Goedecker and Umrigar (GU) are tested in fully variational finite basis set calculations of light atoms, the lowest energy singlet methylene, and, for the first time, potential energy curves of diatomic molecules. Although CH/CHF-style DMFs may give reasonable energies for atoms and molecules near equilibrium geometries, they predict unrealistically shallow minima in the potential energy curves for diatomic molecules with more than two electrons. The calculated CH and CHF molecular dissociation curves exhibit the same patterns of over- and under-correlations as the corresponding correlation energy plots for the homogeneous electron gas undergoing a transition from high to low densities. In contrast, the GU functional yields not only accurate atomic and molecular energies but also plausible dissociation curves. The reasons behind the observed performance are analyzed. © 2002 American Institute of Physics.

Notes: Extensive time-independent quantum mechanical scattering calculations for the H+D2(v=0,j=0) reaction have been performed in the collision energy range 1.39–2.20 eV on the Boothroyd–Keogh–Martin–Peterson potential energy surface. The theoretical differential cross sections (DCS) obtained for the H+D2→HD(v′=3,j′=0)+D channel of the reaction have been compared with recent measurements by Zare and co-workers over the collision energy range 1.39–1.85 eV using the photoloc technique [S. C. Althorpe et al., Nature (London) 416, 67 (2002)]. An excellent agreement between experiment and theory has been found for most of the collision energies studied. In particular, the appearance and evolution of forward scattering with collision energy observed experimentally has been quantitatively reproduced by the theoretical calculations. An analysis of the theoretical results, including a semiclassical complex angular momentum analysis, have been performed in order to ascertain the origin of the sharp forward peaks in the DCS.© 2002 American Institute of Physics.

Notes: Infrared spectra of the weakly bound complexes N2O–4He, N2O–3He, and OCS–3He have been observed using a tunable diode laser to probe a pulsed supersonic jet expansion. The rotational structure of the bands was analyzed using a conventional asymmetric rotor Hamiltonian. The N2O–3He and OCS–3He spectra are mostly a type (ΔKa=0) in structure, with very weak b-type (ΔKa=±1) transitions, but for N2O–4He the a- and b-type components are both prominent. The fitted rotational parameters are consistent with roughly T-shaped structures with intermolecular separations around 3.4–3.5 Å for N2O–He and 3.8–3.9 Å for OCS–He. The angle between the N2O or OCS axis and the He position is about 80° for N2O–He and 65° for OCS–He. The vibrational band origins are slightly blueshifted from those of the free molecule, with the N2O–He shifts (+0.2 cm−1) being about twice the magnitude of the OCS–He shifts (+0.1 cm−1). The results are of particular interest since N2O and (especially) OCS have both been used as probes in experiments on ultracold helium nanodroplets. © 2002 American Institute of Physics.

Notes: Results of the QCICD/6-311++G(3df,3pd) ab initio calculations on the ground state of Ar2H+ are presented. With accurate method and basis sets, the potential energy surface for the ground state was scanned with more than 7000 points, and an analytic global potential energy surface was constructed based on these points. The properties such as the potential minima, the transition state, and the dissociating paths of [Ar–H–Ar]+ were discussed. The influence of the three-body interaction in this system was also investigated, and it is found that a potential based on the two-body additive interaction is not good to represent the Ar2H+ system. © 2002 American Institute of Physics.

Notes: The negative ion photoelectron spectra of the oxide anion complexes O−Rg, Rg=Ar, Kr, and Xe, and O−N2 have been recorded. In each spectrum, two partially resolved peaks were observed, their relative intensities varying with source conditions. These peaks were assigned to photodetachment transitions from the 2Σ ground state and unresolved 2Π3/2,1/2 low-lying excited states of the anion. From our data we find dissociation energies and bond lengths for the 2Σ and 2Π anion states. Periodic trends in the bond length and dissociation energy are examined and compared to those in the isoelectronic neutral halogen rare gas systems and the effect of anisotropy in the interatomic potential and relative interaction strength is examined. From our data we find that the dissociation energies in the anion system are much larger but that the 2Σ-2Π splitting is significantly lower. In addition to the diatomic clusters, we report the photoelectron spectra of the O−Krn=2–5 and O−Xen=2–3 clusters and tabulate the vertical detachment energies and peak widths. From a comparison of the energetics and peak broadening we are able to make a determination of the general structure of the n=2 and n=3 clusters. © 2002 American Institute of Physics.

Notes: A molecular theory of liquid phase vibrational energy relaxation (VER) [S. A. Adelman et al., Adv. Chem. Phys. 84, 73 (1993)] is applied to study the temperature T and density ρ dependencies of the VER rate constant k(T,ρ)=T1−1, where T1 is the energy relaxation time, of model Lennard-Jones systems that roughly simulate solutions of high-mass, low-frequency dihalogen solutes in rare gas solvents; specifically the I2/Xe, I2/Ar, and ICI/Xe solutions. For selected states of these systems, the theory's assumptions are tested against molecular dynamics (MD) results. The theory is based on the expression T1=β−1(ωl), where ωl and β(ω) are, respectively, the solute's liquid phase vibrational frequency and vibrational coordinate friction kernel. The friction kernel is evaluated as a cosine transform of the fluctuating force autocorrelation function of the solute vibrational coordinate, conditional that this coordinate is fixed at equilibrium. Additionally, the early-time decay of the force autocorrelation function is approximated by a Gaussian function which is exact to order t2. This Gaussian approximation permits evaluation of T1 in terms of integrals over equilibrium solute–solvent pair correlation functions. The pair correlation function formulas yield T1's in semiquantitative agreement with those found by MD evaluations of the Gaussian approximation, but with three orders of magnitude less computational effort. For the isothermal ρ dependencies of k(T,ρ), the theory predicts for all systems that the Gaussian decay time τ is nearly independent of ρ. This in turn implies that k(T,ρ) factorizes into a liquid phase structural contribution and a gas phase dynamical contribution, yielding a first-principles form for k(T,ρ) similar to that postulated by the isolated binary collision model. Also, the theory predicts both "classical" superlinear rate isotherms, and "nonclassical" sublinear isotherms similar to those recently observed by Troe and co-workers for azulene relaxation in supercritical fluids. The isochoric T dependencies of k(T,ρ) are studied in the range 300 to 1000 K. For none of the solutions are the rate isochores found to accurately conform to either Arrhenius or Landau–Teller kinetics. © 2002 American Institute of Physics.

Notes: A hybrid quantum-classical computational algorithm, which couples a density functional Hamiltonian to a classical bath, is applied to investigate symmetry breaking and the vibrational spectrum of [NO3]− in aqueous clusters. The nitrate ion was modeled using density functional theory with a Gaussian basis set; two different force fields for the classical bath were investigated: the TIP4P-FQ fluctuating charge and the TIP4P mean-field potentials. The choice of basis sets, functionals, and force field parameters has been validated by performing calculations on small complexes [NO3(H2O)n]− (n=1,2) at 0 K. We have found different asymmetrical configurations, mostly of Cs symmetry, with characteristic lifetimes in the picosecond range in a molecular dynamics (MD) simulation of [NO3 (H2O)124]− using the TIP4P potential. The vibrational density of states (DOS), computed by calculating the Fourier transform of the velocity autocorrelation function, shows two distinctive peaks corresponding to the antisymmetric N–O stretching (around 1500 cm−1) for each configuration, in contrast with the degenerate peak observed in the isolated solute. The DOS corresponding to the whole simulation, in which several configurations were visited, is similar to the broad band observed experimentally in aqueous solution. The structural and DOS results obtained for a TIP4P simulation of [NO3]− solvated with 256 water molecules do not differ significantly from those obtained with the smaller cluster, confirming that the main features of solvation are already present in the smaller system. In order to assess the influence of solvent polarization, we have performed a hybrid simulation employing the fluctuating charge TIP4P-FQ water potential. We obtain similar results to those obtained using the mean-field potential, except that residence times of each asymmetric configuration are larger than in the TIP4P case. © 2002 American Institute of Physics.

Notes: A hybrid quantum mechanical molecular mechanical (QMMM) approach is used to study H3O+, H2O, NH4+, NH3, Cl−, HCl, F−, HF, CH3COO−, CH3COOH, Ag+ and glycine in both zwitterionic and nonzwitterionic forms in water. The free energies of hydration of these species are presented and are shown to compare favorably with experimental values. The difference in water–glycine interaction energy between the zwitterionic and nonzwitterionic forms is calculated as a lower limit and is in line with previous findings. The first theoretical examination of the Ag+–glycine complex in solution is presented. © 2002 American Institute of Physics.

Notes: High resolution polarized absorption spectra of U3+:LaCl3 single crystals were recorded in the 4000–50 000 cm−1 range at 7 K. The experimental crystal-field energy levels of the U3+ ion were fitted to a semiempirical Hamiltonian employing free-ion, one-electron crystal-field as well as two-particle correlation crystal-field (CCF) operators. The performed analysis of the spectra enabled the determination of crystal-field parameters and reassignment of some of the observed 5f3→5f3 transitions. The effects of selected CCF operators on the splitting of some specific U3+ multiplets have been investigated. On the basis of the obtained electronic wave functions the electric-dipole intensity parameters of the total transition dipole strength were determined by fitting the calculated and experimental transition intensities. Among 67 transitions observed in the 4000–22 000 cm−1 range 56 were sufficiently well resolved for quantitative calculations. © 2002 American Institute of Physics.

Notes: The ground-state rotational spectra of the five isotopomers C4H4O(centered ellipsis)H79Br, C4H4O(centered ellipsis)H81Br, C4D4O(centered ellipsis)H79Br, C4H4O(centered ellipsis)D79Br, and C4H4O(centered ellipsis)D81Br of a weakly bound complex formed by furan with hydrogen bromide in the gas phase have been observed with a pulsed-jet, Fourier-transform instrument. Each spectrum was analyzed and fitted to give rotational constants A0, B0, and C0, centrifugal distortion constants ΔJ and ΔJK, and components χaa, χbb-χcc, and χab (or χac in the case of C4D4O(centered ellipsis)H79Br) of the bromine nuclear quadrupole coupling tensor. A detailed analysis of the spectroscopic constants reveals that the observed complex does not have C2v symmetry, with HBr lying along the C2 axis of furan. Instead, the geometry is of the face-on type, with the Br atom of HBr lying close to the perpendicular drawn through the center of the mass of the furan ring. The H atom of HBr lies between the Br atom and the face of the furan ring. The angles αaz made by the HBr internuclear axis z with the a axis has the two possible values ±11.929°. The preferred structure is that generated when the positive value of the angle is chosen and has the HBr subunit pointing in the direction of the O atom of furan. The determined geometrical parameters are r(O(centered ellipsis)H)=2.599(3) Å, φ=112.90(14)°, and θ=6.05(4)°, where φ is the angle made by the O(centered ellipsis)H internuclear line with the local C2 axis of furan and θ is the angular deviation of the O(centered ellipsis)H–Br nuclei from collinearity. Reasons why furan(centered ellipsis)HCl, but not furan(centered ellipsis)HBr, obeys some simple rules for predicting angular geometries are discussed. © 2002 American Institute of Physics.

Notes: Electronic and band structure calculations of SrBe3O4 crystal from first principles are performed based on a plane-wave pseudopotential method for the first time. The linear refractive indices and the static second-harmonic generation (SHG) coefficients are also calculated by the SHG formula improved by our group. The calculated values are in good agreement with the experimental values. A real-space atom-cutting method is adopted to analyze the respective contributions of the cation and anionic groups to the optical response. The results show that the contribution of the (SrO9) group to the SHG coefficients is more pronounced than that of (BeO3)4− and (BeO4)6− groups. Because the plane BeO3 and tetrahedral BeO4 groups have a little covalent bonding, they only give a tenth of the contribution of the SrO9 group. © 2002 American Institute of Physics.

Notes: We report a molecular dynamics investigation of the glass transition temperature in selenium at pressures ranging from 0 to 6 GPa as a function of the quench rate, Qr. For moderate pressures the specific volume of the glass depends strongly on the quench rate, whereas the specific enthalpy varies only little. We find for both volume and energy a linear dependence on the quench-rate-dependent glass transition temperature. The slopes of these curves reflect the different energy scales of void formation, inter- and intrachain interactions. The extrapolated glass transition temperatures for quench rates of order K/s agree with the experimental ones within 20%. Applying a pressure of 1 GPa the glass transition temperature is raised by 37 K. For the same Qr, the transition temperature Tg is much higher for simulations using fixed volume conditions (NVT ensemble) than for the ones using fixed pressure (NPT ensemble) when one compares results for equal pressure at T=0. © 2002 American Institute of Physics.

Notes: We present an efficient transfer matrix formalism for obtaining the quantum conductivity of single-wall carbon nanotubes (SWCN's) based on a nonorthogonal tight-binding scheme. The formalism is used to calculate conductivity in the presence of topological defects and H adsorbates. I-V characteristics show large oscillatory behavior as a function of the number of H adatoms for both (10,0) and (5,5) SWCN's. Furthermore, the conductivity is found to depend sensitively on structural relaxation. © 2002 American Institute of Physics.

Notes: We study submonolayer Ag deposited Ge(001) surfaces at 90 K by scanning tunneling microscopy (STM). Silver atoms and their small aggregates on the surface are found as bright dots on the surface at 78 K. The Ag aggregates form small clusters, and move with the change of the buckling phase in the adjacent Ge dimer row at 180 K as observed in successive STM images. These are transient processes to the formation of a surface alloy between Ag and Ge. © 2002 American Institute of Physics.

Notes: The adsorption of thiolate radicals on the Au24 nanocluster truncated from the Au (111) surface is investigated using first principles electronic structure calculations under the density functional theory formalism. Particular emphasis is given to understanding the chemical interactions at the gold-sulfur interface. In order to describe the influence of the back bonds at the thiolate sites we have carried out adsorption studies with thiophene 2-thiolate (-ST) and thiophen–2-yl-methanethiolate (-SCH2T) along with atomic sulfur (S), mercapto (-SH), and methylthiolate (-SCH3). The results suggest that the adsorption geometry at the gold-sulfur interface is strongly dependent on the local environment of the terminal sulfur atom. The interfacial charge transfer is found to be localized along the Au-S bonds and does not influence the molecular structure of the thiophene ring. © 2002 American Institute of Physics.

Notes: The reaction of CO2 to carbonate CO3δ− is studied on the O-enriched RuO2(110) surface using thermal desorption spectroscopy and high-resolution electron energy-loss spectroscopy. It is known that the epitaxially grown RuO2(110) surface exposes coordinatively unsaturated sites, so-called Ru-cus and O-bridge, and can be O-enriched by dissociative adsorption of O2 giving rise to weakly bound O-cus atoms on top of Ru-cus. CO2 adsorption at 85 K and annealing up to 250 K, results in a stepwise increased carbonate CO3δ− formation which takes place only on Ru-cus sites. Based on isotope substitution experiments the carbonate-related losses are identified among them the symmetric stretching mode at 150.8 meV and the asymmetric one at 174.9 meV. Through interaction of CO2δ− with O-cus, both chemisorbed on neighboring Ru-cus sites, a bidentate transient state and finally a monodentate carbonate CO3δ− is formed. The molecular plane of monodentate CO3δ− is oriented perpendicular to the surface with a tilted RuO–CO2 axis. The maximum carbonate coverage is about 25%. © 2002 American Institute of Physics.

Notes: The electronic properties of Mg-O divacancy defects at the MgO surface obtained by removing of a pair of O and Mg ions from terrace, step, or corner sites have been investigated using an embedded cluster model. Long-range polarization and lattice relaxation effects have been included through a shell model approach. It is demonstrated that all these defects are electron traps: an addition of one electron to a neutral precursor results in a stable paramagnetic center. We calculate relaxed electron affinities, vertical ionization energies, formation energies, and hyperfine coupling constants of these defects and discuss their relevance for the interpretation of experimental results on the nature of paramagnetic electronic defects at the surface of MgO. These results further extend a concept of surface electron traps beyond simple anion vacancies to more general structural features. © 2002 American Institute of Physics.

Notes: The correlated Pariser–Parr–Pople model Hamiltonian for interacting π-electrons is employed for calculating frequency dependent linear polarizability as well as first and second hyperpolarizabilities of linear chain phosphazenes (–P(Double Bond)N–)x (x=3–6). The model parameters for phosphorus and nitrogen are obtained by comparing the theoretical excitation energies with experimental spectra of the known phosphazene systems. The optical gap of the phosphazene oligomers extrapolates to 3.7 eV compared to 2.8 eV of their organic analogs, namely, the polyenes. The linear polarizability of the phosphazene systems are comparable to those of the polyenes. However, the third harmonic generation coefficients are smaller at the same excitation energies. The power law exponent for the third harmonic generation coefficient in phosphazenes is also much smaller than that in polyenes. The second harmonic generation coefficients of the phosphazenes are smaller than those of the push–pull polyenes. Introduction of terminal push–pull groups on phosphazenes does not significantly improve the second harmonic generation response of these systems. © 2002 American Institute of Physics.

Notes: A new mechanism of electron paramagnetic resonance in spherical zinc-blende semiconductor nanocrystals, based on the extended orbital motion of electrons in the entire nanocrystal, is presented. Quantum confinement plays a crucial role in making the resonance signal observable. The mechanism remains operative in nanocrystals with uniaxially distorted shape. A theoretical model based on the proposed mechanism is in good quantitative agreement with unusual ODMR spectra observed in nearly spherical CdSe nanocrystals. © 2002 American Institute of Physics.

Notes: We investigate the complexation of a highly charged sphere with a long flexible polyelectrolyte, both negatively charged in a salt-free environment. Electroneutrality is insured by the presence of divalent counterions. Using molecular dynamics within the framework of the primitive model, we consider different Coulomb coupling regimes. At strong Coulomb coupling we find that the adsorbed chain is always confined to the colloidal surface but forms different conformations that depend on the linear charge density of the chain. A mechanism involving the polyelectrolyte overcharging is proposed to explain these structures. At intermediate Coulomb coupling, the chain conformation starts to become three-dimensional, and we observe multilayering of the highly charged chain while for lower charge density the chain wraps around the colloid. At weak Coulomb coupling, corresponding to an aqueous solvent, we still find like-charge complexation. In this latter case the chain conformation exhibits loops. © 2002 American Institute of Physics.

Notes: Athermal, tethered chains are modeled with density functional (DFT) theory for both the explicit solvent and continuum solvent cases. The structure of DFT is shown to reduce to self-consistent-field theory in the incompressible limit where there is symmetry between solvent and monomer, and to single-chain-mean-field (SCMF) theory in the continuum solvent limit. We show that by careful selection of the reference and ideal systems in DFT theory, self-consistent numerical solutions can be obtained, thereby avoiding the single chain Monte Carlo simulation in SCMF theory. On long length scales, excellent agreement is seen between the simplified DFT theory and molecular dynamics simulations of both continuum solvents and explicit-molecule solvents. In order to describe the structure of the polymer and solvent near the surface it is necessary to include compressibility effects and the nonlocality of the field. © 2002 American Institute of Physics.

Notes: The pulsed field gradient nuclear magnetic resonance method is applied to study self-diffusion of ethane in beds of zeolite NaX for displacements which are orders of magnitude larger than the size of individual crystals. Comparison of the measured diffusivities with those calculated using simple gas kinetic theory indicates that for the same bed of NaX crystals the apparent tortuosity factor in the Knudsen regime is significantly larger than that in the bulk regime. This finding is tentatively attributed to the more pronounced geometrical trapping by surface imperfections in the Knudsen than in the bulk regime. Tortuosity factors, which are much larger in the Knudsen regime than in the bulk regime, were also recently obtained by dynamic Monte Carlo simulation of gas diffusion in various porous systems. © 2002 American Institute of Physics.

Notes: The reactions of electronically excited carbon atoms, C(1D), with ethylene and propylene were studied at three collision energies between 48 and 104 kJmol−1 employing the crossed molecular beam technique. Forward-convolution fitting of our data combined with electronic structure calculations suggests that the reactions proceed via stripping dynamics. Extremely short-lived allene and 1,2-butadiene intermediates decompose via atomic hydrogen emission to yield propargyl and methylpropargyl radicals, respectively. These production routes are of potential importance to form benzene, toluene, and o-/p-xylenes in circumstellar envelopes of carbon stars and combustion flames. © 2002 American Institute of Physics.