ALBERT

Notes: We have studied some consequences of a generalized theory of electrostatic interactions between two macroscopic surfaces immersed in a dilute electrolyte. The ionic interactions close to the two bounding surfaces were supposed to be specifically affected by the presence of the surfaces, leading to a surface contribution to the total free energy density of the system. A functional integral (sine-Gordon) representation of the grand canonical partition function was derived and evaluated in the saddle-point approximation, leading to the repulsive mean-field and an attractive first-order correlation correction to the interaction free energy. The magnitude of the correlation term was investigated in detail and general conditions on the form of the surface-specific free energy density were derived that would lead to an anomalously large exponentially decaying attractive interactions. We present some arguments in favor of the view that this anomalous long-range attraction could well represent a case for the electrostatic nature of the recently measured long-range "hydrophobic'' attraction.

Notes: We have determined the electron spin diffusion constant in (dicyclopentaheptalene)2SbF6 by means of a magnetic field gradient electron spin resonance spin echo technique. Parallel to the chain axis we obtain a value of D(parallel)≈0.064 cm2 s−1. From the comparison of temperature dependent conductivity and susceptibility measurements it is concluded, that the charge carriers are localized in this compound. These localized charge carriers can be described as a system of 1d-Heisenberg spin chains. The measured D(parallel) value therefore corresponds to an effective exchange coupling constant of J≈4.5 meV (J/kB≈51 K).

Notes: We present a spectroscopic study of jet-cooled C3 in which laser-induced-fluorescence (LIF) excitation spectra and dispersed-fluorescence (DF) spectra are taken for a new, vibronically induced band system (1Πg and/or 1Δu)−X˜ 1Σ+g in the ultraviolet. In addition, DF spectra are taken for the well-known cometary band system, A˜ 1Πu–X˜ 1Σ+g. The DF spectra of the new system are very rich and display strong fluorescence bands in stretch–bend progressions that reach as high as 17 000 cm−1 in the 1Σ+g ground state. The data from the DF spectra of both systems is used to assign vibrational term energies to 144 ground-state levels that cover the range: 0≤v1≤8, 0≤v2≤37, and 0≤v3≤4. The observed level structure clearly demonstrates the highly anharmonic nature of the potential energy surface of C3 and the unusual internal dynamics that occurs upon it. These include pronounced barriers to linearity in the v3=2 and v3=4 states and an increase in molecular rigidity as the symmetric stretch is excited.

Notes: The first ESR (electron spin resonance) results are reported for a metal–methylene radical. The CuCH2 molecule was generated by trapping the products of the pulsed laser vaporization of copper in the presence of cyclopropane in neon matrices at 4 K. A second generation procedure involved the laser vaporization of elemental carbon and copper in the presence of H2(g). The unpaired electron in CuCH2 was found to occupy primarily the carbon p orbital which was perpendicular to the C2v molecular plane. This electronic distribution confirms the 2B1 ground state assignment predicted by previous theoretial calculations. The neon matrix magnetic parameters (MHz) were: g⊥=2.000(3); g(parallel)=2.0027(3); 63Cu: A(parallel)=303(1); A⊥=306(1); H:||A(parallel)||=66.6(3); ||A⊥|| =43.1(3) and 13C@B:||Aiso||=124.3(5).

Notes: We report three-dimensional L2 basis-set calculations of eigenvalues and eigenfunctions of CIHCI and IHI for zero total angular momentum. Comparisons are made to previous calculations of resonance energies and the bound state in IHI. These eigenfunctions are used in simulations of the photodetachment spectra of ClHCl−→CIHCI+e− and IHI−→IHI+e−. The spectra are convoluted with Gaussian weight functions as was done in very recent simulations of Schatz, based on coupled-channel scattering calculations, and in the experiments of Neumark and co-workers.

Notes: The stochastic classical trajectory method is used to calculate the energy relaxation of a highly excited diatomic rotor trapped in rare gas crystal at T=20 K. The friction kernels, which appear in the generalized Langevin equations characterizing the motions of the molecule and of nearest neighbor crystal atoms, are expressed in terms of the interaction potentials. The influence of the surrounding crystal on the relaxation mechanism and the efficiency of the various dissipation channels are analyzed by changing the rare gas species and by artificially switching off some channels. Within the limits of the model (classical two-dimensional rotation of the diatomic molecule, coupled on the one hand to a restricted number of first shell atoms themselves coupled to the bulk crystal and on the other hand to the other first shell atoms considered as pertaining to the bath), the results of the calculations show that, in the present case, rotational relaxation is a rapid process, over the picosecond scale, and that the local mode connected to the motions of the molecular center of mass plays a major role in the mechanism. This local mode is responsible, at short times t≤0.5 ps, for the relaxation of 95%, 75%, and 60% of the rotational energy excess in Ar, Kr, and Xe crystals, respectively.The remaining energy is then dissipated over longer times via the local mode or directly towards the crystal modes. A striking energy saturation phenomenon of the local mode is exhibited in xenon crystal.

Notes: A theoretical model was proposed for the orientational effects in diffusion-controlled enzyme reactions. To this purpose, we attained the exact solution of the rotational–translational diffusion equation (RTDE) with mixed boundary conditions (MBC). In steady-state conditions, the assumed MBC were: (i) the reactant molecules are chemically modified at the enzyme active site, provided that their relative orientation lies within a given angular range; (ii) the reactant molecules outside the active site or for uncorrect orientations are reflected; (iii) the concentration of reactants is constant at infinite distance from the active site. The developed exact analytical procedure led to a system of linear algebraic equations, which was numerically solved for the simple case of only one angular variable (plane–rotor approximation). The procedure was found to be well suited to calculate the kinetic constant of the enzymatic as a function of different physical parameters, such as the translational and rotational diffusion coefficients, the range of allowed orientations of the reactants, and the size of the active site of the enzyme.

Notes: The results of a microcanonical variational transition state theory study of the HO2 and HeH+2 systems are reported. The calculations were carried out using a modification of the Wardlaw–Marcus flexible transition state theory method in which the sum of states N(E,R) is calculated directly. For the HO2 system, the results obtained using the Melius–Blintpotential surface are in excellent agreement with previously reported variational transition state theory calculations of Rai and Truhlar on this system. In particular, two transition states were found for the HO2→OH+O half-reaction. However, calculations using the Lemon–Hase surface produced only one transition state. From calculations carried out on surfaces constructed by combining the two original surfaces and calculations carried out using an orbiting transition state variational model (i.e., ignoring the angular part of the potential), it is shown conclusively that the two transition states found for the Melius–Blint surface arise from the peculiar shape of the minimum reaction path for this surface. Also, the orbiting transition state calculationssuggest that phase space theory can describe this half-reaction on the Lemon–Hase surface over a large energy range provided that the potential along the minimum reaction path is used in the phase space theory calculations. Other calculations, in which the parameters of the Lemon–Hase surface were adjusted, were also carried out in order to determine the conditions necessary to support multiple transition states. The results of these calculations suggest that multiple transition states are more likely to occur when a strong bottleneck is present in the angular part of the potential, especially when the intermediate complex exists in a shallow well. These predictions were confirmed by theresults obtained for the HeH+2 system using the McLaughlin–Thompson–Joseph–Sathyamurthy surface. Two transition states were found for the HeH+2→HeH++H half-reaction and calculations using the orbiting model showed that the origin of the multiple transitionstates is not the minimum reaction path as in the case of the Melius–Blint surface. Furthermore, the energy at which "transition state switching'' occurs is in reasonable accord with the energy at which phase space theory calculations begin to diverge from the experimental data on the cross section for this system. Lifetime calculations for the pseudocomplex lying between the two transition states suggest that the observation of multiple transition states may be possible using femtosecond transition state spectroscopy. Finally, calculations on the HeH+2→He+H+2 half-reaction showed that one transition state exists for this half-reaction at low energy, while at higher energy there are no transition states.

Notes: Theoretical calculations have been performed to determine the spectroscopic constants for the ground and selected low-lying electronic states of the transition-metal noble-gas ions VAr+, FeAr+, CoAr+, CuHe+, CuAr+, and CuKr+. Analogous calculations have been performed for the ground states of the alkali noble-gas ions LiAr+, LiKr+, NaAr+, and KAr+ and the alkaline-earth noble-gas ion MgAr+ to contrast the difference in binding energies between the simple and transition-metal noble-gas ions. The binding energies increase with increasing polarizability of the noble-gas ions, as expected for a charge-induced dipole bonding mechanism. We find that the spectroscopic constants of the X 1Σ+ states of the alkali noble-gas ions are well described at the self-consistent field level. In contrast, the binding energies of the transition-metal noble-gas ions are substantially increased by electron correlation. The difference arises from the contribution of metal-neutral noble-gas-ion character in the wave functions. This correlation effect increases as the ionization potential of the noble gas decreases from He to Kr and as the ionization potential of the metal atom increases.

Notes: Propargylene was identified in a matrix as a product of photolysis of cyclopropenylidene and diazopropyne. The molecule is a triplet. The optimum geometry predicted by ab initio calculations corresponds to a structure HC≡C–C¨H. The transition structure in the interconversion HC≡C–C¨H(arrow-right-and-left)HC(overdot)=C=C(overdot)H(arrow-right-and-left)HC¨–C≡CH is very low in energy and close to the energy of the vibrational ground state. Owing to this nonrigidity, computed infrared (IR) frequencies based on a harmonic treatment do not match the experimental spectrum. When this nonrigidity is taken into account by using a nonharmonic approximation calculated UMP2/6-31G** IR spectra are in good agreement with the observed spectra of HCCCH and DCCCD.

Notes: The first-order interaction energy between two He atoms is calculated for a range of interatomic distances with a large explicitly correlated basis set reproducing over 99.998% of the correlation energy of the He atom. The interaction energy obtained in basis sets of increasing size converges to within 0.1 μhartree. This accuracy is comparable to accuracy of calculations which use orbital basis sets of spdfgh quality. Our results agree well with values extracted from experiments. We also show that our largest He wave functions behave properly in the outer region of the He atom.

Notes: The order-by-order perturbation expansion of the effective Hamiltonian for a multireference space is presented. The concept of the general model space (complete or incomplete) of Hose and Kaldor is used as well as their concept of a graphical representation of the perturbation expansion. The obtained result differs, however, from that of Hose and Kaldor. In the Hose and Kaldor derivation many types of disconnected diagrams of the effective Hamiltonian are declared reducible and omitted by in fact they do not completely cancel and these give an irreducible contribution to the effective Hamiltonian maxtrix causing the method to not be fully extensive. To ensure that all terms are included, we present modified diagram rules for the effective Hamiltonian.

Notes: Thermochemical data, ΔH(open circle)n−1,n and ΔS(open circle)n−1,n (n=1–7), of clustering reactions, H+3(Ar)n−1+Ar=H+3(Ar)n and D+3(Ar)n−1+Ar=D+3(Ar)n, were measured with a pulsed electron-beam high-pressure mass spectrometer. The shell formation with n=3 and 6 was observed for both H+3(Ar)n and D+3(Ar)n clusters. The binding energies of D+3(Ar)n are found to be about 0.2 kcal/mol greater than those of H+3(Ar)n with n=1–3. With n≥4, the binding energies for both clusters become about the same. The Ar ligands in the cluster D+3(Ar)n are found to have slightly more restricted freedoms of motion than those in H+3(Ar)n, probably due to the smaller size of the core ion D+3 than H+3. The binding energy of H+3---Ne was also measured. The obtained binding energy (∼0.4 kcal/mol) is more than one order of magnitude smaller than that of H+3---Ar (6.69 kcal/mol). This is mainly due to the much smaller polarizability of Ne than Ar. A careful remeasurement of thermochemical data for the clustering reaction H+3+H2=H+3(H2) was also made. The obtained −ΔH°(7.01 kcal/mol) and −ΔS°(18.1 cal/mol K) values are in excellent agreement with our previous measurement.

Notes: The partition function for the grand canonical ensemble of particles interacting via pairwise potential is presented in the field-theoretic path integral form. The Schwinger-type equation of motion for the above partition function produce in the lowest order approximation the famous mean spherical approximation. Use of the saddle point methods applied to the partition function produces known density functional results. The above field-theoretic form is further generalized to the case when the interaction between the particles depends upon their internal "quantum'' states which are being modeled with the help of Potts-like variables.

Notes: The nonlinear response of a two-state chemical transition to an oscillating electric field is examined. A reaction for which this analysis is particularly relevant is a conformational transition of a membrane protein exposed to an ac electric field. Even a modest externally applied field leads to a very large local field within the membrane. This gives rise to nonlinear behavior. The applied ac field causes harmonics in the polarization and can cause a dc shift in the state occupancy, both of which can be observed and used to determine kinetic parameters. Fourier coefficients are calculated for the enzyme state probability in the ac field, exactly for infinite frequency, and in powers of the field for finite frequency. Kramers–Kronig relations are proved and response functions are given for the leading terms of the harmonics. The results are extended to the spherical symmetry relevant to suspensions of spherical cells, vesicles, or colloidal particles. If the protein catalyzes a reaction, free energy is transduced from the electric field to the output reaction, even if that reaction is electrically silent. Many transport enzymes are ideal examples. The ac field can cause the enzyme to pump ions or molecules through the membrane against an (electro)chemical potential. The efficiency of this energy transduction can be as high as 25%.

Notes: A Smoluchowski equation is derived that depicts the relative diffusion of a sphere with respect to a fixed nonspherical convex body. The transport equation is expressed in terms of the surface-to-surface separation s, measured along the surface normal k. In this coordinate system, the effects of particle shape anisotropy can be subsumed by an appropriate mapping of the radius of the convex excluded volume surface onto that of an equivalent spherical system. Steric effects in diffusion-controlled reaction rates and shape anisotropy corrections to the recollision kinetic theory of rotation are analyzed in light of the chosen coordinates and the explicit Smoluchowski equation.

Notes: Polystyrene spheres with attached functional groups that ionize in solution repel one another; at sufficiently high sphere concentrations the spheres self-assemble into a crystalline lattice with lattice constants large enough to diffract visible light. We have experimentally and theoretically examined diffraction phenomena from colloidal crystals of polystyrene spheres of diameters between 69 and 127 nm in water. We relate the diffraction bandwidths to the sphere scattering powers in the context of the dynamical diffraction theory and demonstrate the importance of the dynamical theory for predicting the observed diffraction angles, intensities, and bandwidths. We also discuss the mechanism contributing to the diffuse scattering and show the significance of the coherent scattering by lattice phonons.

Notes: Sticking of light gas atoms (He,D,H) on the (0001) surface of graphite is studied theoretically in the framework of the quantum mechanical perturbation theory. The formulas include a detailed microscopic description of the solid structure and vibrations. The calculations are employed in conjunction with the published experimental data to investigate the properties of the inelastic gas–surface coupling in the He/graphite system. The inelastic coupling is suggested to have a significant attractive component, and to be confined to highly localized spots on the surface. The low energy sticking probability is shown to be very sensitive to the weak coupling between the graphite layers. The high energy sticking via excitation of the optical out-of-plane phonons is found to be very inefficient. The isotopic effect is investigated in the H,D/graphite system. While the heavy isotope sticks about two times more efficiently in the low energy limit, the decay of the sticking probability with the energy is slower for the lighter isotope. Therefore the difference in the sticking probability of the two isotopes decreases strongly towards higher energies.

Notes: Molecular dynamics simulations have been used to study the structure and dynamics of monolayers of long-chain molecules on a metallic substrate. The system consisted of 90 molecules held at a fixed surface density and periodically replicated in the plane of the surface. Two models have been studied as alternative representations of the admolecule–surface interactions in layers formed by the self-assembly of alkyl thiol [SH(CH2)15CH3] molecules onto a gold substrate. The principal difference between the two models is that in one, the S–C bond is required to lie nearly parallel to the substrate surface. After lengthy equilibration at room temperature, both models yield monolayers in which the chains are aligned and tilted with respect to the surface normal. Although the tilt angle is different for the two models, the thickness of the monolayers is the same and the influence of the "modified-headgroup'' on the detailed structure of the film is confined to the region closest to the metal surface. There are striking differences in the chain rotational dynamics of the two models which are likely amenable to experimental verification.

Notes: The dynamics of chemisorption and decomposition of SiH2 on Si(111)–(1×1) and recontructed Si(111)–(7×7) surfaces have been investigated using classical trajectories on a previously described [Surf. Sci. 195, 283 (1988)] potential-energy surface modified to yield the experimental bending frequencies for chemisorbed hydrogen atoms and to incorporate the results of ab initio calculations of the repulsive interaction between SiH2 and closed-shell lattice atoms. The Binnig et al. model is employed for the (7×7) reconstruction. Sticking probabilities are found to be unity on the (1×1) surface and near unity on Si(111)–(7×7). The major mode of surface decomposition on the (7×7) surface is by direct molecular elimination of H2 into the gas phase. Hydrogen atom dissociation to adjacent lattice sites is a much slower process and the chemisorbed hydrogen atoms thus formed exhibit very short lifetimes on the order of (1.13–10.6)×10−13 s. The calculated rate coefficients for these two decomposition modes are 3.4×1010 and 0.79×1010 s−1 , respectively. The rate coefficients for the corresponding reactions on the (1×1) surface are 6.6×1010 and 5.3×1010 s−1 , respectively. The rates on the (1×1) surface are faster due to the increased exothermicity released by the formation of two tetrahedral Si–Si bonds upon chemisorption compared to a single Si–Si bond on the (7×7) surface. Molecular beam deposition/decomposition experiments of SiH4 on Si(111)– (7×7) surfaces reported by Farnaam and Olander [Surf. Sci. 145, 390 (1984)] indicate that chemisorbed hydrogen atoms are not formed in the SiH4 decomposition process whereas the present calculations suggest that such a reaction, although slow, does occur subsequent to SiH2 chemisorption. It is suggested that energetic differences between SiH4 and SiH2 chemisorption are responsible for these differences.

Notes: The adsorption, thermoreactions, and photoreactions of NO coadsorbed with potassium on Si(111)7×7 at 90 K have been investigated using work-function measurements, high-resolution electron energy loss spectroscopy, and mass spectrometry. A minimum in the work function of Si(111)7×7 at 90 K vs the potassium exposure is observed and it is suggested that higher K exposures passed the work-function minimum result in the formation of K multilayers, which upon thermal heating desorb at 315 K. Submonolayers of potassium introduce a new adsorption configuration of NO on Si(111)7×7 at 90 K. This new NO species exhibits a weak intramolecular bonding and competes with NO adsorbed in other configurations. During thermal heating, this NO species gradually dissociates, thus contributing to N2 recombinative desorption, and at relatively high K coverages leads to desorption of N2 and N2O at 555 K via N2O synthesis from NO. The surface after thermal heating to 〉555 K is depleted of molecular species and covered with atomic N and O. Preferential surface oxidation occurs in the presence of potassium. Under photon irradiation (300–900 nm), desorption of N2, NO, and N2O is observed. The photodesorption intensities decrease monotonically as the K coverage increases. The experiments provide further evidence that the dominant contribution to the three photodesorbed species comes from molecularly adsorbed NO and that N2O is synthesized under photon irradiation.

Notes: Our recently developed RISM integral equation theory of the structure and thermodynamics of homopolymer melts is generalized to polymer mixtures. The mean spherical approximation (MSA) closure to the generalized Ornstein–Zernike equations is employed, in conjunction with the neglect of explicit chain end effects and the assumption of ideality of intramolecular structure. The theory is developed in detail for binary blends, and the random phase approximation (RPA) form for concentration fluctuation scattering is rigorously obtained by enforcing incompressibility. A microscopic, wave vector-dependent expression for the effective chi parameter measured in small angle neutron scattering (SANS) experiments is derived in terms of the species-dependent direct correlation functions of the blend. The effective chi parameter is found to depend, ingeneral, on thermodynamic state, intermolecular forces, intramolecular structure, degree of polymerization, and global architecture. The relationship between the mean field Flory–Huggins expression for the free energy of mixing and our RISM-MSA theory is determined, along with general analytical connections between the chi parameter and intermolecular pair correlations in the liquid. Detailed numerical applications to athermal and isotopic chain polymer blend models are presented for both the chi parameter and the structure. For athermal blends a negative, concentration-dependent chi parameter is found which decreases with density, structural asymmetry, and increases with molecular weight. For isotopic blends, the effective (positive) chi parameter is found to be strongly renormalized downward from its mean field enthalpic value by long range fluctuations in monomer concentration induced by polymeric connectivity and excluded volume. Both the renormalization and composition dependence of the chi parameter increase with chain length and proximity to the spinodal instability. The critical temperature is found to be proportional to the square root of the degree of polymerization in stark contrast to the classical mean field prediction of a linear dependence. Comparison of the theoretical predictions with SANS measurements and computer simulations is presented, alongwith brief discussions of nonideal effects and lower critical solution temperature phenomena.

Notes: The vertical ionization potentials of the D2d and C2v structures of B2H4 are reported at the G1 level of ab initio molecular orbital theory. The results support the interpretation by Ruscic, Schwarz, and Berkowitz of their new photoionization experiment in terms of a C2v bridged structure of B2H4. In addition, the bridged C2v B2H+4 cation is found to have a very small barrier to inversion (1 kcal/mol).

Notes: Molecular beam and temperature programmed desorption (TPD) techniques are used to study the low temperature (85 K) adsorption and subsequent thermal desorption of NH3, HF, and H2O from Au(111). At 85 K the molecular sticking coefficients are near unity and are coverage independent. The TPD spectra are qualitatively different for the various species. Simple hydrogen bonding arguments based on absorbate–absorbate interactions are used to explain the differences in the TPD spectra.

Notes: Reaction cross sections and threshold energies have been determined for the first time for the isotopically pure reaction, H+n-C4H10→H2+C4H9, for abstraction from both the primary and secondary C–H bonds. Reaction probabilities were measured for H atoms at selected initial energies up to 112 kJ mol−1 by a photochemical method. With these results and the data for Xe moderated systems, together with new calculations of H–Xe collision densities by a stochastic method, it was possible to evaluate the cross sections and the corresponding reaction rate coefficients. Cross sections rose from threshold energies of 31±5 and 49±5 kJ mol−1 for secondary and primary abstraction, respectively, to ∼9×10−4 nm2 per secondary C–H bond and ∼5×10−4 nm2 per primary C–H bond at around 100 kJ mol−1. These cross sections are somewhat lower than those for secondary C–H bond in propane, and primary C–H bonds in propane and in ethane, but all are considerably smaller than the total collisional cross section.

Notes: The ground-state energies for helium-like atoms are computed by the Ritz variational method. The trial wave function is chosen to be of the form ψ=[ln(r12+e)+C(r1−r2)2] ×exp[−S(r1+r2)], where r1 and r2 are the distances of the electrons from the nucleus, r12 the distance between the electrons, e the natural base of logarithms, and the parameters C and S are determined by minimizing the energy of the atom. The numerical results are presented and compared with those of other authors.

Notes: Experiments on the reflection of polarized monochromatic laser light at the planar interface of resonantly absorbing medium and the air were made for a variety of situations, including Brewster's angle in the spectral vicinity of the resonance wavelength. An ethanolic solution of Rhodamine B, an organic laser dye luminofor with a well defined resonance absorption spectrum, was chosen as the absorbing medium. The tunable polarized output of a cw dye laser was used to provide the collimated monochromatic beam. To compare the experimental results with theory, the Fresnel reflectivity equations combined with the Kramers–Kronig relations were used to predict the reflectance in terms of the known absorption coefficient. The experimental results generally confirm the theoretical predictions.

Notes: Optically detected magnetic resonance experiments have been conducted at pressure up to 45 kbar for p-dichlorobenzene (DCB), s-tetrachlorobenzene (TCB) and quinoxaline (Q). The pressure dependence of their zero-field splitting parameters and, for DCB, the quadrupolar splitting are reported. For all three systems the D value decreases moderately with increasing pressure. The slope for TCB is approximately twice that for DCB. These results are interpreted in terms of pressure dependence of the mesomeric effect and the inductive effect of the substituents on the aromatic triplet state. For Q, the influence of pressure on spin-orbit interaction is also suggested.

Notes: Effects of vibronic coherence transfer induced by the heat bath on ultrafast time-resolved resonant light scattering (RLS) spectra are theoretically investigated within the master equation approach. The vibronic coherence initially created by a coherent optical excitation transfers to other vibronic coherent states due to inelastic interactions between the vibronic system concerned (the relevant system) and the heat bath. The vibronic coherence transfer results in the quantum beats in the time-resolved RLS spectra. The bath-induced vibronic transition operator is derived in the double space representation of the density matrix theory. Model calculations of the femtosecond (fs) time-resolved RLS spectra are performed to demonstrate the effects of the bath-induced vibronic coherence transfer.

Notes: The shapes of spectral lines obtained by a series of four-level infrared–infrared double-resonance experiments in 15NH3 have been used to obtain information about the collisional transfer of energy in this molecule. In these experiments a CO2 laser has been used to pump a near-resonant vibration–rotation transition in the ν2 band while an infrared microwave sideband laser system scans a vibration–rotation transition in the 2ν2←ν2 band. When the k quantum numbers in the pump and probe are such that Δk=3n, where n is a positive or negative integer, the probe transition is a superposition of a Gaussian part and a transferred spike. When Δk≠3n, only the Gaussian part is observed. The widths of the transferred spike for ||Δk||=3 and 6 transitions, which have been observed for the first time in this work, are substantially greater than the width of the spike observed for Δk=0 transitions. Theoretical expressions are given for the line shape of the transferred spike and for the ratio of the intensities of the two components of the double resonance. The line shapes have been used to estimate the root-mean-square change in velocity upon collision for Δk=0 and ||Δk||=3 transitions. The results of three-level double resonance measurements in which a ν2 fundamental transition is pumped while a 2ν2←ν2 transition is probed are also reported. The widths of the three-level double resonance for copropagating and counterpropagating beams are significantly different and the results of simulations to reproduce the line shapes and their implications for collisional energy transfer are discussed.

Notes: Information about the unimolecular acetylene (HC 3/4 CH)↔vinylidene (H2C=C:) isomerization on the S0 energy surface has been extracted from vibrationally unassigned high resolution stimulated emission pumping (SEP) spectra of acetylene. The combination of a new pattern recognition scheme, spectral cross correlation (SCC) with complete nuclear permutation-inversion (CNPI) group theory is shown to be a powerful new technique for characterizing bond rearrangement in highly vibrationally excited normally rigid polyatomic molecules. SCC detects isomerization "resonances'' which destroy an approximate vibrational symmetry (e.g., the number of cis-bending quanta). The energies (relative to the zero point level of the stablest isomer) and widths of such resonances provide information about the "energies'' of isomer rovibrational levels and the isomer-level-specific isomerization rate. Vinylidene isomerization resonances may be distinguished from ordinary acetylene Fermi or Coriolis perturbations by a unique rotational symmetry dependence due to the correlation between acetylene [D∞h(M)] and vinylidene [C2v(M)] levels in the CNPI group G8. An SCC map of the HCCH S0 15 000–15 900 cm−1 energy region above the zero point level was obtained by comparing SEP spectra recorded via S1(A˜ 1Au)33 and 2162 Ka=1 intermediate levels. The predicted rotational symmetry dependence of the SCC was found between 15 410–15 640 cm−1, but the vinylidene resonance line shape was obscured by Franck–Condon interference effects from well known perturbations between the 33 and 2162 SEP intermediate levels. It was therefore not yet possible to determine the height of the isomerization barrier (or even whether a barrier exists) but an upper bound for the vinylidene zero point level of 15 525 cm−1 was inferred from the SCC data.

Notes: A semiclassical model for tunneling from one classically allowed region on a potential energy surface to another is described. The principal feature of this model, compared to earlier (more "rigorous'') multidimensional semiclassical tunneling theories, is that it can be implemented in a straightforward way within the framework of a standard classical trajectory simulation. Applications to several examples of unimolecular isomerization and unimolecular dissociation show that the model is capable of providing excellent results over a wide range of conditions (i.e., coupling strengths, different symmetries of couplings, etc.)

Notes: Novel modeling and sensitivity analysis techniques are used with experimental data obtained from discharge flow–resonance fluorescence experiments to evaluate the product branching ratio of OH+H2CO. Two channels are considered: the H-atom abstraction reaction (R2) to form HCO and H2O; and the addition reaction (R17) followed by rearrangement and decomposition to form HCOOH and H. The rate constant values obtained at 298 K are kR2 =(7.75±1.24)×10−12 cm3/molecule s and kR17=(0.2+0.8−0.2) ×10−12 cm3/molecule s. The results demonstrate that the reaction proceeds almost exclusively via the H-atom abstraction pathway.

Notes: The Hamiltonian-based model developed by the authors [N. J. Cotes and M. G. Sceats, J. Chem. Phys. 89, 2816 (1988)] for bimolecular reactions which exhibit severe configurational restrictions, such as orientational requirements for reaction at surface sites, provides an analytical expression for the reaction rate which involves the evaluation of the potential of mean force along the radial coordinate that describes the binding. The expression for the reaction rate is evaluated for the case of a charged molecule interacting with a binding site on a dipolar particle. The results of the model are compared with the multidimensional Brownian-dynamics simulations of Northrup et al. [J. Chem. Phys. 84, 5536 (1986)] and excellent agreement is obtained in the diffusion limit.

Notes: Absolute rate constants for quenching and intramultiplet mixing of Hg(63P0,1,2) by collisions with H2, HD, and D2 have been determined. A smooth variation of these coefficients with the isotopic form of hydrogen has been observed. For He only an upper limit of the rate constants has been obtained. Attempts to explain the 3P1←3P2 transfer by simple mechanisms are described. The surface crossing mechanism seems the most adapted. But a theory more elaborate than the one presented here should be developed, including both the rotational and the vibrational degrees of freedom of the molecule.

Notes: Ab initio molecular orbital calculations at the G1 level of theory have been carried out on neutral B2H5 radical, doubly bridged B2H+5 cation, and the first triplet excited state of B2H+5. Singly bridged B2H5 is 4.0 kcal/mol (without zero-point energies) more stable than doubly bridged B2H5. Based on this work and previous theoretical work on triply bridged B2H+5, ionization potentials (vertical and adiabatic) are determined for B2H5. The adiabatic ionization potentials of the two B2H5 structures are 6.94 eV (singly bridged) and 7.53 eV (doubly bridged). A very large difference is found between the vertical and adiabatic ionization potentials (3.37 eV) of the singly bridged B2H5 structure. The first triplet state of B2H+5 is found to be 4.55 eV higher in energy than the lowest energy B2H+5 cation (triply bridged). The results of this theoretical study support the interpretation of Rušcic, Schwarz, and Berkowitz of their recent photoionization measurements on B2H5.

Notes: A new algorithm for the calculation of molecular integrals involving STOs is reported. The algorithm enables us to obtain every two-center one-electron integral and the long-range many-center one- and two-electron integrals. The efficient implementation of the algorithm is discussed and its performance is thoroughly tested. The analysis on the stability of the relations employed in the calculation of multipolar moments is included. Futhermore, the computer time required to carry out each step (construction of basic matrices, calculation of multipolar moments, and calculation of two-electron integrals) has also been analyzed. The range of validity of this approach is shown in several molecular integrals.

Notes: The connected moments expansion with use of variational Monte Carlo technique (CMX-VMC) is applied to the calculation of the ground state energies of H, H−, Be, and Li2. Exponential-type wave functions for H, Hylleraas-type wave functions for H−, and a Hartree–Fock single determinant constructed with a single-zeta Slater-type orbital multiplied by a pair correlation factor of Jastrow-type for Be and Li2 are employed as approximate trial wave function. The results of the present computation are found to agree with the corresponding exact values quite well. The overlap between the approximate and exact wave function is also estimated simultaneously by the new technique.

Notes: The bond-orientational order in molten salt LiF, KF, and KCl systems has been studied by molecular dynamics simulation. The bond spherical harmonics have been calculated for the instantaneous local structures in computer-generated configurations of the molten salts. A new method of bond spherical harmonics calculation with equal neighbor number N has been proposed. For the standard structures with different coordination number, their quadratic invariant Ql histograms with same N have been calculated and a model with parameter of square deviation have been suggested. The Ql histograms with N=4 and N=12 for some standard structures have been given and the qualitative or semiquantitative estimations of the bond-orientational orders in those three molten salt systems have been obtained. The bond angle probability distributions have also been calculated and taken as the basis for evaluating the usefulness of the new method. The results show that the local structures in molten salt systems are somewhat similar to tetrahedron while the icosahedron structure is hardly found.

Notes: The experimental vapor phase nucleation data of Nuth et al., for silver [J. A. Nuth, K. A. Donnelly, B. Donn, and L. U. Lilleleht, J. Chem. Phys. 77, 2639 (1982)] and SiO [J. A. Nuth and B. Donn, J. Chem. Phys. 85, 1116 (1986)] are reanalyzed using a scaled model for homogeneous nucleation [B. N. Hale, Phys. Rev. A 33, 4156 (1986)]. The approximation is made that the vapor pressure at the nucleation site is not diminished significantly from that at the source (crucible). It is found that the data for ln S have a temperature dependence consistent with the scaled theory ln S≈ΓΩ3/2 [Tc/T−1]3/2, and predict critical temperatures 3800±200 K for silver and 3700±200 K for SiO. One can also extract an effective excess surface entropy per atom Ω=2.1±0.1 and an effective surface tension σ≈1500−0.45T ergs/cm2 for the small silver clusters (assuming a range of nucleation rates from 105 to 1011 cm−3 s−1). The corresponding values for SiO are Ω≈1.7±0.1 and σ≈820−0.22T ergs/cm2 (assuming a range of nucleation rates from 109 to 1012 cm−3 s−1).

Notes: A new exact trajectory surface-hopping procedure is presented. The method is used to run test calculations on two classic (Landau–Zener– and Demkov-type) atom–atom systems. Transition probabilities as a function of impact parameter show an excellent agreement with quantal results.

Notes: A theoretical model for the infrared (0–1) band of dilute solutions of diatomic polar molecules in nonpolar rare-gas liquids is presented. The model is based on decomposition of the rotational motion of the diatomic molecule into two limiting cases, according to the Bratos model: quasifree rotation and rotational diffusion. Contribution to the infrared absorption coefficient due to quasifree rotation is analyzed within a non-Markovian formalism using a stochastic directing intermolecular field (DIF) model to describe the diatomic molecule–solvent interaction. The P and R branches appear as a consequence of the quasifree contribution, which is also important in the Q-branch region. The contribution due to rotational diffusion is calculated making use of the Debye model and is mainly significant in the Q-branch region.

Notes: We have performed scattered light intensity autocorrelation measurements on a Winsor type microemulsion system composed of brine, cyclohexane, SDS and a mixture of 1-butanol and 1-pentanol. At high cosurfactant concentration, where the microemulsion phase was considered to consist of individual, spherical water-in-oil droplets of relatively low droplet volume fraction, the autocorrelation functions were observed to be essentially single exponential, as expected. Above a certain droplet volume fraction, however, additional decay modes were observed to enter the correlation data. These modes were interpreted to be due to rotation and/or internal motion of droplet aggregates.

Notes: The electronic spectra of silyl radicals, SiH3 and SiD3, were observed between 310 and 430 nm (46 000–64 000 cm−1) by resonance enhanced multiphoton ionization (REMPI) mass spectroscopy. The spectra were generated through a 2+1 REMPI mechanism. Two Rydberg series originating from planar, D3h point group states were observed. One series, of quantum defect δ=1.45(2), is comprised of the E˜ 2A‘2(4p), J˜ 2A‘2(5p), and M˜ 2A‘2(6p) Rydberg states which have origins at ν0–0 =48 438, 56 929, and 60 341 cm−1 in SiH3 and at ν0–0 =48 391, 56 874, and 60 267 cm−1 in SiD3. In SiD3 theP˜ 2A‘2(7p) Rydberg origin was observed at ν0–0 =62 002 cm−1. The H˜, K˜, and N˜ states observed in the SiD3 spectrum comprise the second Rydberg series, δ=2.09, and were tentatively assigned as ns 2A'1 Rydberg states (n=5, 6, 7). The K˜ and N˜ origins were observed at ν0–0 =58 417 and 61 005 cm−1. A fit of the Rydberg formula to the np 2A‘2(n≥5) origins found the adiabatic ionization potential of the SiH3 and SiD3 radicals to be IPa=8.135(+5,−2) eV and IPa=8.128(1) eV, respectively. Detailed vibrational analyses of these Rydberg states are presented. Analysis showed that in the E˜ 2A‘2 (4p) state of the SiH3 radical ω2 (a‘2 symmetric bend)=796(7) and 2ω4 /2(e' degenerate bend)=870(5) cm−1 and that in SiD3 radical ω'1 (a1 SiH3 symmetric stretch)=1576(3), ω'2 =589(3), and 2ω4 /2=635(6) cm−1. The REMPI spectra exhibited ν‘2 hot bands from vibrational levels as high as Ev =2073 cm−1 in the X˜ 2A1state. Modeling calculations, which fit the numerous ν‘2 hot bands, predicted barriers to inversion of Binv=1935 cm−1 and Binv =1925 cm−1 for SiH3 and SiD3 X˜ 2A1 radicals, respectively.

Notes: A high degree of structure and therefore order in chaos is found to exist in the detailed dynamical pathways to conformational isomerization. It is shown that this structure can be used to determine the probabilities associated with the dynamical pathways to reaction, trapping, and back reaction. An earlier publication described the mediation of the dynamics of 3-phospholene by phase space structures we called "reactive islands'' (RIS)21. In this paper we extend the physical and mathematical properties of RIS and develop the corresponding kinetic theory. RIS theory is applied to a model of a hindered rotor and 3-phospholene. It is shown that the RIS kinetic model accurately predicts trajectory simulations of conformer population decay. Comparisons with standard RRKM theory are included. A discussion on the extension of RIS theory to quantum reactive dynamics and its relevance to laboratory experiments is also included.

Notes: Pulsed neutron diffraction measurements have been made on liquid 1,2-dichloroethane-d4 (DCE). The wide momentum-transfer range (∼0.3–50 A(ring)−1) available has been used to further refine previously measured molecular structure parameters as well as to test the validity of the inelasticity corrections applied. A measurement using chlorine isotopes on a steady (reactor) source served to partially separate the chlorine–chlorine and the chlorine–carbon plus chlorine–deuterium correlations. The isotopic difference curves were then analyzed and the relevant features of the distribution of internal dihedral angles [P(τ)] obtained by adequate inversion of the experimental difference–functions. The intermolecular pair correlation function was then derived and both sets of functions (from pulsed and steady sources) are compared and tentatively assigned.

Notes: Brownian dynamics computer simulations are used to investigate the shape of the mean-squared end-to-end distance distribution function in the three regimes: (1) excluded volume; (2) θ; (3) collapsed. It is found that Mazur's function fits regime (1), that the Gaussian function fits regime (2), and that neither of these appear to describe the collapsed state. The implications of these results to theories of ring formation during polymerization is pointed out.

Notes: Periodic variations of an external parameter or constraint of open chemical systems have been shown to induce changes in time averaged kinetic and thermodynamic quantities. We examine the effects of the analytic form of the periodic variation on the time averaged quantities and find the maximum changes obtainable through periodic variations. A variational procedure is proposed, based on a Fourier expansion of the form of the periodic perturbation, the laws of thermodynamics, conservation of matter, and the kinetics. The efficiency of power production in a combustion system is examined with this method in a numerical example. A unique maximum in the efficiency is found, with the gains achievable for more complex functions exceeding those for a sinusoidal perturbation. We interpret the changes in efficiency in terms of the magnitude of the response of the system (resonance) and phase shifts between the periodic perturbations and the response of the system. We illustrate the mechanisms of efficiency changes in this system with two examples; one in which the periodic perturbation affects the phase relations and one in which the periodic perturbation affects the magnitude of the response. Finally, we note that multiple attractors may coexist in this system for certain forms of the periodic perturbation, each with a distinct efficiency.

Notes: Monte Carlo simulations using statistical perturbation theory (SPT) were applied to calculate the free energy, solvation enthalpy, and partial molar volume changes for transforming the solute methylamine to methanol in an aqueous solution of 264 water molecules. Using preferential, as well as random, sampling the calculated thermodynamic parameters were compared in the averaging phase after considering 1500 and 3000 K configurations. The relative free energy shows little variance after taking 1500 K configurations. The solvation enthalpy and the partial molar volume agree well with the experimental values after taking 3000 K configurations for methanol and 4500 K configurations for methylamine. There are 3.0 to 3.3 water molecules in the first hydration shells of the polar groups of the solutes with ∼2 of the waters involved in hydrogen bonds with methylamine and ∼2.4 hydrogen bonded to methanol. The calculated numbers of hydrogen bonds do not change after taking 1500 K configurations, and coordination numbers of the polar sites with water were stable after 3000 K. The similarity of the solution structures with the two different solutes suggests little difference in the solvation entropy in accordance with experiment.

Notes: Video-LEED, HREELS, TDS, and Δcursive-phi measurements were used to investigate the adsorptive, structural, and vibrational properties of the Ru(101¯0)/H system between 100 and 500 K. At all temperatures investigated hydrogen adsorbs dissociatively with very high initial sticking probability (s0(approximate)1.0) with apparent precursor mechanism. The saturation coverage at 100 K is extraordinarily high (aitch-thetamax =2(approximately-equal-to)1.728×1015 H atoms cm−2), up to this coverage four H binding states α, β1, β2, and β3 can be distinguished having desorption energies between 56 KJ/mol (α) and 80 KJ/mol (β3). The H binding states are intimately correlated with the four observable ordered H phases: At aitch-theta=1 a c(8×2) or "1×2'' structure with weak split spots appears which transforms at higher coverages into a clear 1×2 phase with likewise weak spots and with maximum intensity at aitch-theta=1.2. It follows a c(2×2)-3H phase (I maximum at aitch-theta=1.5) with rather more intense ‘extra' spots which fade away with increasing coverage until at aitch-theta=2.0 a (1×1)-2H pattern is reached. The (positive) H-induced work function change Δcursive-phi runs through two maxima and saturates at ∼250 mV. The vibrational loss spectra which were measured in two perpendicular azimuths exhibit a variety of bands which can be correlated with the ordered H phases and point to H species bound in two different kinds of threefold coordinated sites. Our data suggest several structural similarities with the neighboring system in the periodic table, Rh(110)/H, but also interesting differences.

Notes: Novel rigorous upper and lower bounds, at primitive level, to general electron-repulsion integrals (ERIs) involving Gaussian basis sets have been derived and interconnections with the earlier works in the literature are brought out. New optimal strategies for a preemptive elimination of insignificant ERIs at atom and contraction levels are discussed and tested, resulting in a significant reduction in CPU time. Similar analysis is carried out for the computation of the molecular electrostatic potential for the first time in the literature, leading to a marked savings in computer time.

Notes: The molecular crystal 1,2,4,5-tetrabromobenzene (TBB) has been studied using Brillouin scattering and lattice dynamical calculations. A method for mapping acoustic mode anharmonicity is developed that exhibits substantial directional behavior and correlates well with the directions of the molecular movements associated with the phase transition. It is shown that by comparing the calculated sound velocities with the experimental values, insight can be gained into the displacive phase transition and the lattice dynamics of TBB. The sound velocities are plotted for three crystallographic planes containing the crystal axes. The relationships between sound velocities and lattice dynamics are discussed. The phonon dispersion curves for three directions are also presented.

Notes: The absorption spectra of high-n Rydberg states of methyl iodide and benzene perturbed by varying number densities of hydrogen or argon, range 0.9×1020–10.5×1020 cm−3 for H2 and 0.6×1020–7.5×1020 cm−3 for Ar, have been investigated. The high-n molecular states of both absorbers were found to shift linearly with the number density of atomic Ar and molecular H2 scatterers. The Fermi formula modified by the Alekseev–Sobel'man polarization term provides an excellent fit of the shift data. The electron scattering lengths obtained are: 0.93 a0 for H2 and −1.63 a0 for Ar using the CH3I absorber; and 0.99 a0 for H2 and −1.57 a0 for Ar using the C6H6 absorber. The electron scattering lengths for H2 and Ar agree with the results of an empirical model that correlates scattering lengths and the polarizabilities α(spherical) for inert atoms and α2(nonspherical) for H2 molecule.

Notes: Theory based on a configuration coordinate model is presented to clarify solute–solvent relaxation effect on the line shape of a time-resolved hole-burning spectrum. The time-resolved hole-burning spectrum is affected by both a hole created in a ground-state population and an excess excited-state population. The solute–solvent relaxation causes thermalization in both populations and then the shift and broadening of the spectrum is expected observable. The line shapes of three typical cases are mainly considered: (1) The excited state is assumed to have an infinitely long lifetime; (2) the excited state has a finite lifetime, the population being assumed to relax toward an electronic state other than the ground state, and (3) the population created in the excited state relaxes to the ground state, where a hole-filling effect is taken into account. Results obtained by numerical calculations show that a time evolution of the ground-state hole is clearly observed when the low-energy tail of the absorption band is excited under the condition that the population decay to the other electronic state is very fast. Further, it is predicted that the hole-filling effect causes a considerable deformation of the spectral shape when the solvent relaxation rate is comparable to the excited-state population decay rate.

Notes: We present an overview of the discrete variational method for calculating orbital states of a molecular cluster in the local density approximation. Then we introduce a new method of embedding a finite molecular cluster in a crystal lattice. This new technique of cluster weighting is based on the bulk stoichiometry of the crystal and the Mulliken populations for chemically complete atoms—those atoms that have all their covalently bonded nearest neighboring atoms also in the cluster. We have applied our new approach to calculate linear-combination-of-atomic-orbitals ground states for seven copper oxide crystals and Cu metal. The average net Mulliken charges calculated for Cu atoms in this way are shown to correlate well with the observed energies of the Cu K edge feature in x-ray absorption spectra of these materials. Several of these compounds are important to understanding the high Tc superconductivity of copper oxides.

Notes: The first-order phase transition of the ferromagnetic Ising model driven by the magnetic field at temperatures below criticality is studied by Monte Carlo methods for a two-dimensional thin film geometry, L×M with two free boundaries of length M(very-much-greater-than)L, at which boundary fields act. This model study is relevant, in particular, for phase transitions in monolayers adsorbed at stepped surfaces. While in the bulk geometry (L→∞) this transition occurs for zero field in the present model, with the system "jumping'' from a state with uniformly positive magnetization to a state with uniformly negative magnetization, in the thin film geometry the transition occurs at a critical field H*∼L−1, and the two states between which the transition occurs are characterized by strongly nonuniform magnetization profiles across the film. These findings are in agreement with the scaling theory of Fisher and Nakanishi.

Notes: The theory for determination of molecular alignment from circular dichroism in photoelectron angular distributions is generalized to treat the case in which the excitation polarization direction and the laboratory z axis do not coincide. A new method of data analysis is presented here. Alignment created by surface scattering or photofragmentation should be obtainable by these procedures. For studies of orientation with elliptically polarized excitation, differential cross sections at a given collection angle are found to be, to a good approximation, independent of excited-state alignment. Orientation can thus be obtained from differential cross sections by the methods developed by Kummel, Sitz, and Zare [J. Chem. Phys. 88, 6707 (1988)].

Notes: A molecular dynamics simulation of a realistic model of neopentane [C(CH3)4] in its plastic phase has been performed on a sample of 6×6×6 fcc unit cells (i.e., 864 molecules) at 135, 175, and 230 K. The molecules of the simulated sample interact through phenomenological exp-6, atom–atom potentials between all the atoms of nearest neighbor molecules. The orientational probability density function (opdf), the displacement probability density function (dpdf), and its second moment the Debye–Waller factor have been computed. We confirm the very large value and the important thermal variation of the Debye–Waller factor and the strong anisotropy of the opdf deduced from neutron diffraction experiments. The computed opdf is very well reproduced by a mean-field calculation making use only of the microscopic intermolecular potential and of the equilibrium position of the molecular centers of mass, a result in line with the isotropic character of the dpdf, but not valid for other plastic crystals made of molecules with different geometries.

Notes: Molecular dynamics simulations of the freely jointed effective hard sphere model of a polymer melt are performed, with continuous covalent and noncovalent potentials employed for computational convenience. The virial theorem is used to determine the melt pressure from the simulations. Excellent agreement is found over a wide range of density and degree of polymerization with the recently introduced equation of state of Honnell and Hall. The atomic pressure is defined as the contribution made by each atom to the compressibility factor of the system; it is found to be uniform along the interior atoms of the polymer chain, with slightly different values for the end atoms. This uniform value is almost independent of N, the number of bonds in the chain, and explains the small dependence on N of the pressure that is observed. Particular attention is paid to the contribution to the pressure made by the force in the covalent bonds of the system. For packing fractions greater than 0.3, approximately 30% of the pressure in the melt arises from this source.

Notes: The system of a fluid in the presence of a spherical semipermeable vesicle (SPV) with the freely mobile nonpermeating species inside the vesicle is investigated via an integral-equation approach. This system can be used to model certain feature of a biological cell, permeable to simple ions, in which solute proteins inside the cell are unable to permeate its walls. As an illustrative example of the use of our integral equations, the analytical solution for density profiles in the mean-spherical approximation/Debye–Hückel approximation (MSA/DH) is obtained, where the MSA is used to obtain the density profiles near a membrane and the DH approximation to obtain the bulk pair correlation functions. A method which applies to nonmobile protein fixed inside a cell is also considered.

Notes: Kr clusters produced in a supersonic nozzle expansion have been studied by electron impact ionization mass spectrometry. Mass resolved spectra (with n up to 180) show two homologous series consisting of Kr+n and Kr2+n ions. The distribution of Kr+n ions shows distinct magic number effects, the observed abundance anomalies being very similar to the ones observed in Ar and Xe. This confirms the superior stability of closed-shell and -subshell icosahedral structures. Moreover, we have found evidence for the occurrence of Kr3+n and Kr4+n ions. It was possible to determine appearance sizes of these multiply charged cluster ions (yielding n2=69, n3=156, and n4=264), and to study the electron energy dependence of singly and doubly charged cluster ions (yielding a linear threshold law). These results are discussed in view of various theoretical considerations and previous results where available.

Notes: A nearly symmetric critical mixture (φc=0.486) of perdeuterated and protonated 1,4-polybutadiene exhibiting an upper critical solution temperature Tc=61.5±1.5 °C has been quenched from the homogeneous state ((approximately-equal-to)75 °C) to various temperatures between 25 and 57.5 °C. Light scattering measurements document the subsequent spinodal decomposition process which we describe based on a four-stage model: early, intermediate, transition, and final. The early stage is accounted for by the Cahn theory, yielding initial correlation lengths and effective diffusion coefficients in quantitative agreement with mean-field predictions. Nonlinear effects mark the beginning of the intermediate stage, which exhibits a simple power-law growth of heterogeneity length Lm(t)∼tneff, but with a temperature dependent exponent neff. As the composition fluctuation amplitude approaches the equilibrium values, the spinodal decomposition process enters the transition stage, characterized by a decreasing interfacial thickness and an increasing Lm(t). Once the interfacial profile equilibrates, a crossover to the final stage occurs. Subsequent growth of L(t) leaves the morphology unaffected as evidenced by a universal structure factor. These findings are discussed in the context of the current theory and are compared with prior studies involving polymer–polymer and simple liquid mixtures.

Notes: A theory is presented which accounts for "giant'' enhancements in electron stimulated desorption (ESD) yields from adsorbate-covered surfaces if the incident electrons become trapped in a shape or Feshbach resonance associated with the adsorbate. The resulting temporary negative ion is displaced inwards towards the surface as a result of the force provided by the image screening charge. Upon reneutralization, the "desorbate'' can be returned high on the dissociative repulsive wall of the neutral-surface potential curve. This process has been modeled within the context of semiclassical Gaussian wave packet dynamics. Recent observations of such giant enhancements in the ESD yields for the system O(a)/Pd(111) are explained in terms of this model, and an atomic physics basis for the resonance in atomic oxygen is proposed.

Notes: Laser-induced fluorescence of the NCN radical was observed downstream of a microwave discharge of N2 and CF4 in He via the A 3Πu–X 3Σ−g transition near 329 nm. The zero-pressure fluorescence lifetime of the 000 vibrational level of the A state was measured from the time-resolved laser-induced fluorescence to be 183±6 ns. Other spectral features were observed both to the blue and red of the 000–000 band. The blue-shifted features are tentatively assigned to the 020–000, 100–000, 030–010, and 110–010 vibrational bands. Quenching cross sections were determined for NCN (A 3Πu, 000) at 300 K for Ar, Kr, Xe, O2, CO, CO2, N2O, SF6, NO, and NO2. The molecules He, N2, and CF4 are inefficient quenchers and upper limits only were obtained. The large variation in cross section among the colliders does not correlate with predictions of simple electronic quenching models.

Notes: The rheological properties of silver metal liquid-like films, trapped between two immiscible liquid phases, were investigated by measuring laser light scattering from the interfacial capillary waves using optical heterodyne mixing spectroscopy. All the films studied were found to have small elasticities in the range 0.27 to 1.0 dyn/cm. These values are consistent with a colloidal model of the structure of the films with diffusional processes possibly short circuiting the interfacial stresses. It also indicates a gaseous state, consistent with the charge of the surfactants and the silver colloidal particles, and the strong effect of perfluorosurfactants.

Notes: The permanent electric dipole moments for the X 5Π and B 5Π states of gas-phase chromium monoxide, CrO, have been experimentally determined using the sub-Doppler optical technique of intermodulated fluorescence spectroscopy in conjunction with the Stark effect. The measured values are 3.88±0.13 and 4.1±1.8 D for the X 5Π and B 5Π states, respectively. The theoretical values determined for the X 5Π state, using multireference configuration interaction iterative-natural-orbital and finite-field calculations, are in excellent agreement with the experimental value.

Notes: The microwave spectrum of dichlorosilylene SiCl2 has been observed to characterize this molecule of chemical interest. The molecule was generated by the thermal reaction between silicon powder and tetrachlorosilane at about 1000 °C. The rotational constants and the centrifugal distortion constants were determined for the three isotopic species Si35Cl2, Si35Cl37Cl, and Si37Cl2. The nuclear quadrupole coupling constants were determined from triplet hyperfine splittings observed for several transitions. The asymmetry of the Cl nuclear quadrupole coupling tensor was found to be very large and was accounted for by π electron backdonation from Cl to Si.

Notes: The spectrum of the linear carbon chain molecule C5 in the gas phase has been studied around 2170 cm−1, the region of the highest asymmetric stretching vibration ν3. The results were obtained using a tunable diode laser spectrometer and a cooled hollow cathode discharge in a flowing mixture of acetylene and helium. Four vibration–rotation bands were assigned and analyzed: the fundamental, a hot band arising from the v7=1, l=1 vibrational level, a second hot band arising from v7=2, l=0, and a third hot band tentatively ascribed to v5=1, l5=1. Small local perturbations were found to affect the upper vibrational states of two of the bands. Analysis of the data yielded accurate values for a number of molecular parameters for C5, e.g., the band origin ν3= 2169.4410(2) cm−1, the rotational constant, B0 =2557.63(9) MHz, and the l-type doubling parameters, q7=3.99(6) MHz, and q5=2.36(9) MHz. The value of q7 may be used to estimate a value of 118 cm−1 for the lowest bending frequency of the molecule. There is no evidence in C5 for quasilinear behavior such as that shown by C3 and C3O2.

Notes: The title theorem follows from formally equivalent time evolutions of the bounded systems' quantum wave function described by the Schrödinger equation, and regular classical trajectories described by corresponding Hamilton's equations. Instructive model applications include dynamics of molecules with time-dependent Hamiltonians, e.g., intramolecular vibrational energy redistributions, and state selective vibrational transitions induced by periodic sub-ps IR laser pulses.

Notes: We report converged quantum mechanical calculations of scattering matrices and transition probabilities for the reaction of H with H2 with total angular momentum 0, 1, and 4 as functions of total energy in the range 0.85–1.15 eV on an accurate potential energy surface. These calculations show energy dependences that may be attributed to dynamical resonances with vibrational quantum numbers (100 0) and (111 0). The resonance structure is illustrated with Argand diagrams, and we present state-to-state reactive collision delay times and lifetimes. For J=0, 1, and 4, we found the lowest-energy H3 resonance at total energies of 0.983, 0.985, and 1.01 eV, respectively, with lifetimes of about 16–17 fs. For J=1 and 4 there is a higher-energy resonance at 1.10–1.11 eV; for J=1 the lifetime is about 4 fs and for J=4 it is about 1 fs.

Notes: High-order spectroscopic data for the reactant are used exclusively to determine both the sum of open reactive channels and the density of states, which are used in a statistical theory to predict dissociation rate constants. Practical methods are introduced for calculating sums of reactive channels and densities of states, when couplings among all degrees of freedom are included. An empirical method is described for reconciling spectroscopic parameters with known dissociation energies (also determined spectroscopically). The predicted k(E,J)'s and thermal k∞(T) for NO2 dissociation are in good agreement with experimental data, especially when the effects of electronically excited states are included. The predicted low pressure thermal rate constants are generally in fair agreement with experiment, although a slightly different temperature dependence is calculated; this discrepancy is probably due to the absence of unknown higher order spectroscopic terms and to the crude corrections made for excited electronic states. When high order spectroscopic (or theoretical) data are available and when the effects due to excited electronic states are considered, this theory is useful for predicting, fitting, and interpreting unimolecular rate data.

Notes: Absolute total cross sections for collisional electron detachment and collision-induced dissociation (CID) have been measured for binary collisions of SF−6 and SF−5 with rare gas and SF6 targets for laboratory collision energies ranging from about 10 up to 500 eV. The cross sections for electron detachment of SF−6 are found to be surprisingly small, especially for the SF6 target, for relative collision energies below several tens of electron volts. Specifically, detachment onsets are found to occur at around 30 and 90 eV for the rare gas and SF6 targets, respectively. The CID channel which leads to F− as a product is observed to dominate detachment for relative collision energies below 100 eV. The results for the SF−5 projectile are remarkably similar to those exhibited for SF−6. The role of long-lived excited states in the reactant SF6 ion beam is discussed.

Notes: Dissociation of O2 stimulated by soft x-ray absorption has been studied by using a monochromatized synchrotron radiation and a time-of-flight mass spectrometer. The parent molecular ion O+2 was formed only at 531 eV (excitation of 1s→1πg), and a fragment ion O+ had the highest intensity in all the energies giving core–hole states. The measured time-of-flight spectra were reproduced by a simulation calculation, which provided kinetic energy distributions of O+ and O++. The dissociation pathways from the core–hole states of O2 were discussed using the obtained kinetic energy distribution and ion intensity ratios as well as Auger electron spectra in the literature.

Notes: The general theory for inelastic scattering of molecules 1Δ electronic states is outlined and applied to the specific case of 1Δ states arising from a π2 electron occupancy, e.g., NH(a 1Δ). Integral cross sections for rotational transitions out of the lowest rotational level (J=2) of NH(a 1Δ) v=0 are reported for several targets. A pulsed beam of rotationally cold NH(a 1Δ) was produced by 193 nm photolysis of a dilute mixture of hydrazoic acid in nitrogen seed gas at the tip of a nozzle. The target beam was also prepared as a pulsed supersonic beam. The final rotational state distribution was measured in the collision zone by laser fluorescence excitation. The state-to-state cross sections were found to decrease significantly with increasing final rotational quantum number J'. The magnitude of the J=2→J'=3 cross sections were compared for the different targets. Isotopic scrambling in NH(a 1Δ)–D2 collisions was also searched for but not observed.

Notes: The yield of metastable oxygen atoms through dissociative recombination of O+2 ions with electrons has been studied using a plasma flow tube experiment. For O+2 with high vibrational excitation (around v=9) it was found that half of the oxygen atoms are formed on the O(1D) state and that the branching ratio toward O(1S) is large (∼0.4). Using Xe+ instead of Ar+ as precursor ions, it was shown that the O(1S) yield is much less for ions with low vibrational excitation. However, the present experimental results are not compatible with the extremely low theoretical value of this yield which was reported recently for O+2 (v=0).

Notes: Quenching and vibrational energy transfer in the B2Π state of the NS free radical have been studied using temporally and spectrally resolved laser-induced fluorescence in a low-pressure discharge flow reactor. The collision partners were He, Ar, H2, N2, O2, SF6, CO2, and N2O. Total removal cross sections show an oscillatory behavior with v' in the range of unperturbed levels, v'=4–7, for all colliders studied save O2 where a nearly monotonic increase is seen. Vibrational transfer occurs for H2 and the polyatomics; the rates vary little with v'. Δv=2 transfer occurs with the polyatomic colliders for v'=5. Fluorescence decay traces from the perturbed v'=3 and 8 levels differ from the unperturbed levels and from each other. v'=3 is perturbed by quartets and shows "gateway'' level behavior whereas v'=8 is perturbed by a doublet and shows efficient interelectronic transfer for all rotational levels.

Notes: State-to-state charge–transfer cross sections have been computed for N+2(X;v=0,1,2) +Ar at 12 collision energies between 1.2 and 320 eV. A classical path method is used, whereby the vibronic degrees of freedom are treated quantum mechanically as the system moves along a classical trajectory. The calculations use the potential energy surfaces computed by Archirel and Levy. Comparison is made with experimental results for this system, including the recent work from Ng's laboratory. In most cases the agreement is quite good. There is, however, a significant difference in the charge–transfer branching ratios to produce Ar+(2P3/2) or Ar+(2P1/2) products. Possible explanations of the discrepancy are discussed. As expected, the cross sections obey the Franck–Condon principle at energies above 200 eV.

Notes: Second virial coefficients as function of temperature are computed for the title molecular systems interacting with He, Ne, and Ar. The relevant anisotropic forces are obtained via accurate potential functions tested earlier through the analysis of several, different properties of the various systems. The relevant quantum corrections are also computed, in addition to the classical results, and their effects analyzed vis à vis the available experimental data. The influence of such corrections on the very low-T behavior of the virial coefficients and on the determination of the Boyle temperatures is also shown and discussed. All examined potential functions are found to yield B(T) values in rather good accord with experiments, in spite of their marked differences in anisotropic behavior and in the shape of their potential well regions.

Notes: The reaction between ground state atomic oxygen and acetylene was studied using the crossed molecular beam method with an average collision energy of 6 kcal/mol. The two major primary reaction channels are (a) formation of CH2 and CO and (b) formation of HCCO and H. Product angular distributions and time-of-flight spectra were measured and the translational energy release was determined for each channel. The reaction proceeds primarily on the triplet surface through a long-lived intermediate. For both channels the translational energy distributions were found to peak at about 30% of the total available energy, indicating the existence of an exit channel barrier in each case. The branching ratio between channel (a) and (b) was found to be 1.4±0.5.

Notes: A pump-and-probe technique is utilized to yield a population distribution over the rotational quantum states of the nascent product MgH in the reaction of Mg(1P1) and H2. The resulting normalized profile of the MgH bimodal distribution at 693 K coincides with that at 733 K, as well as with the results obtained at 380 K by Breckenridge and co-workers. This temperature dependence demonstrates that the bimodality actually results from the insertive reaction alone. This conclusion is consistent with the isotopic effect.

Notes: A procedure for determining the interaction tensor orientations and the interaction parameters for mutually oriented electric field gradient (efg) or dipolar and shielding tensors has been developed based upon the magnetic field dependence of the critical frequencies from the polycrystalline nuclear magnetic response (NMR) spectrum. The central transition line shape of half-integer quadrupolar nuclei in the presence of mutually oriented shift anisotropy and second order quadrupolar interaction is discussed for the first time. Analytical expressions for the field dependent critical frequencies have been determined for special orientations when the shift principal Z axis lies on the XZ, YZ, or XY plane of the efg (or dipolar) tensor for the first order as well as the second order interactions. The plots resulting from the analytical expressions provide a convenient graphical approach in determining approximate tensorial orientations and interaction parameters through pattern recognition. For general orientations, a numerical procedure has been developed to determine these parameters by iteratively minimizing the squares of the differences of the calculated and the experimental critical frequencies. Higher order perturbation terms can be incorporated in the present treatment. The method is demonstrated by variable field static proton spectra of trichloro–acetic acid at three different fields (1.3, 2.3, 5.2 T). The near-orthogonal orientation between the dipolar and shielding tensors and the interaction parameters obtained from this approach are consistent with those obtained previously from single crystal studies.

Notes: Raman scattering in liquid (and in some cases in solid) isotopic mixtures of HC1 and DC1 is analyzed to prove recent theories by Bratos and Tarjus [Phys. Rev. A 32, 2431 (1985)], Logan [Mol. Phys. 58, 97 (1986)], and Knapp [J. Chem. Phys. 81, 643 (1984)] on vibrational line broadening in liquids. The concentration and temperature dependencies of isotropic [Ji(ω)] and anisotropic [Ja(ω)] line shapes have been studied between triple point (Tt) and critical temperature (Tc). It has been found that in accordance with the Bratos–Tarjus theory, Ji (ω) is much more sensitive of isotopic composition of the liquid than Ja(ω). An analysis of the concentration dependence of the broadening parameters near Tt illustrates the importance of cross correlations between the environmental broadening and the resonant intermolecular coupling. The spectral activity of three-particle resonant transfer also becomes significant. From the change of the maximum of Ji(ω) with isotopic dilution, which is a linear function of mole fraction, the dipole moment derivative δμ/δq is estimated to be more than twice that of its gas phase value. The asymmetry of the isotropic bands of both HC1 and DC1 changes with concentration at constant temperature. With increasing temperature, Ji(ω) of pure and diluted samples narrows as T−0.5 and T−0.3, respectively. Ji(ω) has been found to be intermediate between the slow and the fast modulation limit. From the high frequency wing of Ji (ω) the time constant of the zeroth order memory function was obtained. Its activation energy increases with increasing T. This is in qualitative agreement with the temperature dependence of the Enskog collision time and the spin–rotational correlation time. Taking into account the results of the Bratos–Tarjus theory, orientational correlation times τ(2) are determined from Ja (ω). The Raman method yields τ(2) values which are twice as long as those determined from NMR relaxation.

Notes: The phenomenon of aerodynamic enrichment of heavy molecules seeded in supersonic free jets has been known since 1955. But its systematic exploitation in the generation of intensely focused molecular beams has been prevented by the lack of a quantitative and realistic explanation of the observed facts. Here, the aerodynamic focusing of CBr4, W(CO)6, and C2Cl6 molecules seeded in jets of He or H2 is studied experimentally, and found to be most singular under conditions similar to those known to produce sharply focused beams of microscopic spheres suspended in air jets. The gas mixture expands through thin-plate orifice into a vacuum chamber, forming a supersonic free jet. The spacial distribution of the heavy molecules in the jet is measured at varying distances L to the nozzle by scanning a thermocouple probe across a jet diameter. The probe is sufficiently small to interfere negligibly with the flow. The increment DV in the thermocouple voltage resulting from seeding the heavy gas on a given flow of He or H2 is seen to be a sensitive indicator of the local concentration of seed molecules in the jet. The following behavior is observed in terms of the same Stokes number or inertia parameter S that governs the simpler and better understood phenomenon of aerosol focusing. Below S=0.4 for H2 and S=0.2 for He, heavy molecule and aerosol beam widths are practically identical, and the boundary of the jet of heavy molecules is rather sharp. At higher values of S, aerosol beams show further reductionsin cross section, down to less than 10% of a nozzle throat diameter dn. In contrast, the measured heavy species minimal beam widths or waists at a distance L∼dn from the throat are around 0.5dn and 0.35 dn for jets of He and H2, respectively. In units of dn, these widths are several times larger than expected from elementary considerations on the defocusing effects due to Brownian motion (of the order of the square root of the molecular mass ratio between light and heavy molecules). Nonetheless, the thin-plate orifice nozzle yields considerably more concentrated jets of heavy gases than previously seen, with far-field enrichment factors for the seed species close to 50 in thecase of H2 jets. This technique, thus, appears to provide a greatly improved source for intense molecular beams. Aerodynamically focused beams have a sharp distribution of kinetic energies, being ideally suited for cross beam and beam surface studies. But they are not quite so optimal for spectroscopic studies because they require moderate source Reynolds numbers (of order 100), at which the heavy gas undergoes very little translational, rotational, or vibrational cooling.

Notes: We show that an invariance of a system of N particles simplifies the solution of the classical equations of motion.A transformation can be constructed in a straightforward manner to yield a set of active and redundant coordinates in which Hamilton's equations are separable. That is, the redundant coordinates are cyclic and the kinetic energy is block diagonal between the two sets. Furthermore, the active coordinates have properties very similar to the parent Cartesian coordinates; e.g., the derivatives of the Hamiltonian remain unchanged. The numerical application of the procedure is very straightforward; we have performed trajectories of symmetric motions of an A2B-type molecule within the subspace of the C2v configurations.

Notes: Using recent ab initio interaction potential energy surfaces for the CN (X 2Σ+, A 2Π)+He system [H.-J. Werner, B. Follmeg, and M. H. Alexander, J. Chem. Phys. 89, 3139 (1988)], we have calculated fully quantum cross sections for inelastic transitions between individual rovibrational levels of the A 2Π and the X 2Σ+ states of CN. We have concentrated on the transitions studied experimentally by Dagdigian and co-workers for CN+Ar, namely transitions between the rotational levels of the A, v=8 and X, v'=12, the A, v=7 and X, v'=11, and the A, v=3 and X, v'=7 vibrational manifolds. In the case of the 8→12 and 7→11 transitions the cross sections are large (0.1–1 A(ring)2), and the dependence on initial Λ doublet level and on final rotational quantum number displays the same subtle alternations as seen experimentally. In the case of the 3→7 transitions, for which the vibrational levels are energetically much more separated, the calculated cross sections for CN+He are extremely small (10−5 A(ring)2), far smaller than observed experimentally for CN+Ar. In order to resolve this discrepancy, we have carried out some additional ab initio calculations for the CN+Ar system, but the change in the interelectronic coupling potential appears not to be large enough to explain the magnitude of the experimental cross sections.

Notes: The multiconfigurational spin tensor electron propagator approximation to the electron propagator is applied for the first time to the calculation of electron affinities. The electron affinities of Li, Na, and K are calculated as the ionization potentials of the negative ions. On average these electron affinities differ from experiment by 0.003 eV, giving the best theoretical values reported to data.

Notes: Fermi contact spin densities have been theoretically determined for the ground-state diatomic first-row hydrides CH, OH, and NH having open shell π electrons. Multiconfiguration self-consistent-field wave functions include the dominant configuration and single excitations from it describing the most important spin and orbital polarization effects. Optimization of the orbitals by precise numerical grid methods shows that this simple wave function model is capable of providing spin densities in satisfactory agreement with experiment. Gaussian basis sets suitable for use with this wave function model are determined by comparing to the precise numerical spin density results. Huzinaga's popular (9s5p||4s) primitive Gaussian basis provides a good starting point if augmented with diffuse and polarization functions and with a tight (high exponent) s function at hydrogen. Only the innermost few primitive functions may be contracted. Contraction coefficients may be determined on the basis of free atom Hartree–Fock calculations. These studies lead to economical contracted Gaussian basis sets that should be useful for spin density calculations on larger polyatomic radicals.

Notes: The 363.8 nm (3.408 eV) photoelectron spectrum of the NH2 (X˜ 2B1)+e−←NH−2(X˜ 1A1) transition of the amide anion is reported. The electron affinity of amidogen is found to be EA(NH2) =0.771 ±0.005 eV. P, Q, and R rotational branches are observed in the spectrum; a simple model which accounts for the band structure is presented.

Notes: When a Ne:CO2 sample was codeposited at approximately 5 K with a beam of neon atoms that had been excited in a microwave discharge, an absorption appeared at 1421.7 cm−1, very near the gas-phase band center for the antisymmetric stretching fundamental (ν3) of CO+2. Detailed isotopic substitution studies support the assignment of this absorption to that fundamental of CO+2, as well as of an absorption at 1658.3 cm−1 to ν3 of CO−2. In earlier studies of the charge transfer interaction of an alkali metal with CO2, this vibration of CO−2 had been strongly perturbed by coordination with the alkali metal cation. In the present experiments, the threshold for electron photodetachment from CO−2 was observed in the visible spectral region. Evidence was also obtained for the stabilization of the O2C⋅⋅⋅OCO− cluster anion.

Notes: Three-dimensional microstructures of surfactant–water–oil systems self-assemble in a Monte Carlo lattice model, as shown here. The microstructures that form depend on the volume ratios of oil, water, and surfactant, and on the length of the surfactant, and on the ratio R of the length of the oil-loving to the water-loving portion. For R=1 we find lamellar phases when the surfactant is mixed with equal amounts of oil and water. The lamellar spacing increases as the surfactant concentration is lowered. In the presence of water only, as the surfactant concentration is lowered the microstructure evolves from lamellar to broken lamellar to cylinders to spheroids. This progression is found to be independent of lattice size for lattices as large as 40×40×40. For R=3, the progression seems to be replaced by a progression from lamellae to regular bicontinuous structures to cylinders, although we are not yet confident that this latter progression is independent of lattice size effects. The Monte Carlo technique can be used to study a wide variety of interesting phenomena, from micelle size and shape transitions to packing transitions and phase behavior to interfacial properties in the presence of surfactant.

Notes: The hard sphere system is discussed with the focus on geometry. Three types of exact relations are derived: (i) purely definitional; (ii) definitional and geometric; and (iii) definitional, geometric, and thermodynamic. This careful separation allows a critical study of the statistical thermodynamics of hard spheres. In particular, a geometric Gibbs equation is derived containing only the fundamental geometric parameters of the system, and a set of exact "rules'' can be derived from this equation restricting the behaviors of the fundamental parameters over the entire density range. The geometric Gibbs equation (and the rules) are useful in the derivation of the thermodynamic equation of state, but such application is reserved for a following paper.

Notes: Incoherent neutron scattering (INS) experiments were performed on semioriented samples of n-nonadecane C19H40 and of the selectivity deuterated derivatives CD3–C17H34–CD3 and C2D5–C15H30–C2D5 over a wide temperature range, in particular, over the domain of existence (295–305 K) of the disordered "rotator phase'' RI. From analyses of the inelastic and quasielastic parts of the spectra, we were able to discriminate between motions parallel or perpendicular to the main long-chain axis. In the low frequency region (0–300 cm−1), numerous lattice and internal vibrational modes, showing pronounced polarization effects, were assigned. In the quasielastic regions, large broadenings were observed in the RI phase, providing clear evidences of both fast restricted translational motions along the chain axis and uniaxial rotational diffusions. For the rotational process, we have elaborated and made use of a model of diffusion for a particle in a twofold potential. Finally, the INS spectra of C19H40 in the RI phase and of C23H48 and C24H50 in their RII phases were compared and nicely interpreted within an unique model of "effective potential'' by fitting the barrier heights against rotational diffusion. All these results are discussed and compared to literature data.

Notes: Ultrasonic absorption and velocity measurements have been performed in aqueous solutions of ethoxyethanol and n-butoxyethanol in the frequency range of 5–250 MHz and from about 50 °C to the respective melting temperatures (TM). The latter system exhibits a closed loop of miscibility with a LCST at TC=49 °C. The overall behavior of the absorption looks, in general, similar to previously investigated alcohol–water systems and critical binary mixtures. However, it shows two main characteristic features: (a) a noticeable increase of amplitude and dispersion of the peak values as the temperature decreases toward TM; (b) a weak critical anomaly which is seen only at the lowest frequencies and in a narrow temperature interval around TC. A comparison with the frequency and temperature predictions by the Romanov–Solov'ev fluctuation model and by the Ferrell–Bhattacharjee dynamic scaling theory for critical mixtures shows that the observed spectra near TM cannot be explained by critical-like phenomena. The occurrence of pseudocritical fluctuations, which extends their influence from TM to higher temperatures up TC, is suggested.

Notes: Viscosities of dilute solutions of linear poly(2-vinyl pyridine) with molecular weights ranging from 3.0×104 to 1.0×106 have been measured under conditions where the polymer can be charged by protonation. By employing weakly acidic solvents, large reduced viscosities typical of polyelectrolytes in low-salt solutions are observed. They exhibit a pronounced maximum occurring at a concentration which is independent of molecular weight. Separate pH titrations are used to calculate polyion charge density and electrostatic screening lengths. The origin of the viscosity maximum is explained by consideration of changing electrostatic persistence lengths on dilution, resulting in polyion coil expansion and contraction. Investigations of limiting conditions of low charge density and full electrostatic screening with basic and high acid or salt solutions reveal expected normal polymer behavior in concentration extrapolations to the intrinsic viscosity.

Notes: Three-dimensional computer simulation is carried out for the aggregation process of colloids using the sticky sphere model proposed in the previous paper. Time evolution of the structure of aggregates and macroscopic viscosity is studied when a shear flow is started in a suspension of the sticky spheres. In the transient state, the viscosity is found to increase in sigmoidal manner in agreement with real experiments. This phenomena is shown to be caused by the cooperative aggregation. In the steady state, it is found that (i) as the volume fraction increases, the structure transforms from compact cluster to loose network; (ii) the infinite network appears above the volume fraction about 0.1. and this value is rather insensitive to the shear rate; (iii) below and above the percolation transition, the steady state viscosity depends on the shear rate γ(overdot) in the same power law.