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  • 1
    Electronic Resource
    Electronic Resource
    Spectroscopic signatures of bond-breaking internal rotation. I. Saddle point induced polyad breakdown (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 250-261 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: With the input of order 10–20 000 cm−1 of vibrational energy, the hydrogen atoms in small gas-phase molecules such as HCN, HCP, and acetylene can undergo internal rotation about the heavy-atom core (CN–CP–CC), breaking and reforming covalent bonds in the process. This article investigates the quantum and classical dynamics of covalent bond-breaking internal rotation, particularly the vibrational energy flow between the hindered internal rotor mode and a stretch mode. The aim is to relate polyad effective Hamiltonian techniques, which have been highly successful in the analysis of high overtone spectra, to the theory of isomerization rates. That is, as approximate constants of motion, polyad numbers constrain vibrational energy flow, and we investigate the extent and mechanism of their breakdown due to nascent bond-breaking internal rotation. Our simple model consists of a spherical pendulum coupled to a harmonic oscillator, which admits a number of analytical results. The central conclusion is that polyad breakdown is a generic consequence of higher order resonances induced by a saddle point but is far from complete, in the sense that the majority of states with energies close to the saddle point can continue to be labeled with polyad numbers; only those with substantial probability density close to the saddle point itself no longer belong to moderately well defined polyads. Our model is particularly relevant to the vibrational structure of HCP, the polyad structure of which has been well studied up to ∼19 000 cm−1; our model predicts systematic polyad breaking at higher energies. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330238
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  • 2
    Electronic Resource
    Electronic Resource
    Photoionization of [(η-C6H6)2Cr] with the explicit continuum B-spline density-functional method (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 306-319 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The cross section and asymmetry parameter profiles of (C6H6)2Cr have been calculated with a method based on the density-functional theory with an explicit treatment of the continuum wave function, with a single center basis set of B-spline functions and with an exchange-correlation potential with the correct Coulomb asymptotic behavior. The method has proven efficient from the outer valence states up to the metal and carbon core. The results are in good agreement with the available experimental data, and suggest that important features, not yet measured, should be present in the high-energy range of the valence and core profiles. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328399
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  • 3
    Electronic Resource
    Electronic Resource
    Integral equation study of liquid hydrogen fluoride (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 355-362 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Liquid hydrogen fluoride is a well-known hydrogen bonded substance, in many aspects related to liquid water, and for which a wide variety of interaction models have recently been proposed. We have studied two of these models by means of a reference hypernetted chain equation in order to assess the ability of this latter approach to describe the properties of this highly associative system. Our calculations, when compared with molecular dynamic results, show that the integral equation reproduces quantitatively both the structure and the thermodynamics of liquid hydrogen fluoride over a wide range of thermodynamic states. However, the integral equation approach is apparently unable to produce estimates for the phase diagram since the low-density (gas phase) side of the binodal curve lies inside the nonsolution region of the equation. This failure can be understood as the result of the inability of standard integral equation theories to account for the behavior of low density strongly associative systems like highly charged electrolytes or, in this case, the gaseous phase of hydrogen fluoride. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328758
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  • 4
    Electronic Resource
    Electronic Resource
    A Monte Carlo study of symmetry breaking of I3− in aqueous solution using a multistate diabatic Hamiltonian (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 367-376 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A model for the description of the electronic ground state of the triiodide ion in solution is developed. It is based on the "diatomics in molecules" technique and is parametrized from experimental data. The solvent molecules are treated by classical intermolecular potentials. The solvent–ion interaction, which depends on the instantaneous positions of the solvent molecules, enters into the Hamiltonian matrix elements as a spatially varying external electrostatic potential. We use the model to investigate the distribution of the bond lengths of a linear triiodide ion in water at 300 K using Monte Carlo calculations. We find that under these conditions the molecule is significantly distorted with considerable redistribution of charge and bond lengths of 2.95 Å and 3.38 Å. The free energy barrier to switching bond lengths at room temperature is quite high (of the order of 10 kT) so that the distortion is predicted to have a long lifetime. The distribution of instantaneous vibrational frequencies is investigated and shows that the solvent has a greater effect on the frequency of the antisymmetric stretch than on that of the symmetric stretch vibration. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328757
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  • 5
    Electronic Resource
    Electronic Resource
    Using mean field theory to determine the structure of uniform fluids (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 416-425 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The structure of a uniform simple liquid is related to that of a reference fluid with purely repulsive intermolecular forces in a self-consistently determined external reference field (ERF) φR. The ERF can be separated into a harshly repulsive part φR0 generated by the repulsive core of a reference particle fixed at the origin and a more slowly varying part φR1 arising from a mean field treatment of the attractive forces. We use a generalized linear response method to calculate the reference fluid structure, first determining the response to the smoother part φR1 of the ERF alone, followed by the response to the harshly repulsive part. Both steps can be carried out very accurately, as confirmed by computer simulations, and good agreement with the structure of the full Lennard-Jones fluid is found. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329881
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  • 6
    Electronic Resource
    Electronic Resource
    Stoichiometry changes by selective vacancy formation on (110) surfaces of III–V semiconductors: Influence of electronic effects (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 445-451 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: We investigated the kinetics of thermal formation of anion vacancies and the subsequent stoichiometry changes on (110) cleavage surfaces of III–V semiconductors by scanning tunneling microscopy. We found that the rate of spontaneous formation of monovacancies depends very sensitively on the doping of the underlying semiconductor and the concentration of surface vacancies. It is shown that the position of the Fermi energy at the surface is the major electronic influence on the energy barrier height for the vacancy formation. We found barrier heights in the range of 1.1–1.3 eV for GaAs and InP. The physical factors affecting the vacancy formation and the surface stoichiometry are discussed in detail. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328412
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  • 7
    Electronic Resource
    Electronic Resource
    Eley–Rideal reactions between H atoms on metal and graphite surfaces: The variation of reactivity with substrate (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 474-482 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Results are presented for the reaction of gas-phase H atoms with H atoms adsorbed onto a variety of substrates. Time-dependent quantum methods are used to compute reaction cross sections and product H2 rotational and vibrational distributions for a large number of model potential energy surfaces. The potentials which model reactions on metals exhibit a wide range of reactivity. In addition, the single-collision Eley–Rideal reaction cross sections are generally small, suggesting that hot-atom processes should in general play an important role in H2 formation on metal surfaces. These observations are consistent with recent experiments. Eley–Rideal reactivity is shown to increase as the strength of the H-substrate bond decreases, and H atom trapping becomes less favorable. The cross sections for the reaction of H(g) with H adsorbed onto model graphite surfaces are generally large (5–10 Å2). © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1328041
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  • 8
    Electronic Resource
    Electronic Resource
    Rovibrationally inelastic scattering of (v=1, j=1) H2 from Cu(100): Experiment and theory (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 495-503 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: A comparison between experiment and theory is performed for the scattering of (v=1, j=1) H2 from Cu(100) at normal incidence. Experimentally, this system was studied using molecular beam techniques, with stimulated Raman pumping employed to overpopulate (v=1, j=1) in the incident beam, and resonance enhanced multi-photon ionization used to detect the H2 scattered in two (v=1, j) states, and two (v=0, j) states. Theoretically, six-dimensional wave packet calculations were performed, employing a new, extended potential energy surface that was computed with density functional theory, using the generalized gradient approximation and a slab representation of the metal surface. Theory and experiment are in good agreement for the survival probability, i.e., the probability for rovibrationally elastic scattering. However, the theory overestimates the probabilities for rotationally inelastic scattering (to v=1, j=3) and for rovibrationally inelastic scattering (to v=0, j=5 and 7) for channels that could be determined experimentally. The cause of these discrepancies is discussed, as are possibilities for future improvements in the theory as well as the experiment. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330728
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  • 9
    Electronic Resource
    Electronic Resource
    Vibrational modes of c(4×2) CO–Pt(111) from first-principles calculations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 530-534 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The vibrational modes of CO adsorbed on Pt(111) in the c(4×2) structure have been studied within the harmonic approximation, using density functional calculations. The characters, fundamental energies, and dipole activities have been determined for all modes. For top-adsorbed molecules, the static adsorbate–adsorbate interaction is found to induce energy splitting among frustrated lateral translational modes, which have previously been assumed to be degenerate, and a reassignment of previously measured vibrational energies to low-energy modes is proposed. For bridge-adsorbed molecules, the frustrated rotational fundamental transitions, which should be dipole forbidden from the local adsorption site symmetry, are found to be weakly dipole active. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1330729
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  • 10
    Electronic Resource
    Electronic Resource
    Aggregation kinetics in two dimensions: Real experiments and computer simulations (2001)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 114 (2001), S. 520-529 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The aggregation of silanized glass spheres (75±5 μm diam) was studied experimentally at liquid–air (water–air, aqueous surfactant solution–air, and aqueous glycerol solution–air) interfaces from a kinetic point of view. The number, the size, and the polydispersity of clusters was investigated as a function of time. Particles having water contact angles of (approximate)30° (lower hydrophobic sample) and (approximate)82° (higher hydrophobic sample) were prepared and used in the aggregation experiments. In the early stage of aggregation the kinetics was found to be of the second order. The experiments revealed that the increasing particle hydrophobicity increased the rate constants in every case, which could be attributed to the increasing particle–particle attractions and the decreasing hydrodynamic resistance of particles (clusters) to motion. Moreover, the lower hydrophobicity of particles manifested itself in a more important polydispersity of clusters and an unexpected cross-over during the growth. The cluster–cluster aggregation was succeeded by a particle- (large) cluster aggregation after the first (initial) part of the growth. An off-lattice computer simulation of cluster-cluster aggregation, based on molecular dynamics, was also developed for the better understanding of the interfacial aggregation. The simulations supported well the conclusions derived from the real experiments, and gave an indispensable possibility for the study of the effect of single parameters on the complex phenomenon. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1329344
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