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22 Jan 2003

Volume 118, Issue 4, pp. 1577-2017

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Phonon dispersion curves in KOD-doped ice observed by neutron scattering

Hiroshi Fukazawa, Susumu Ikeda, Mitsugu Oguro, Stephen M. Bennington, and Shinji Mae

J. Chem. Phys. 118, 1577 (2003); http://dx.doi.org/10.1063/1.1539846 (4 pages) | Cited 5 times

Online Publication Date: 8 January 2003

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We measured the inelastic neutron scattering (INS) of a single crystal of KOD-doped D2O ice, and investigated the dispersion curves in a proton-ordered phase of ice Ih (ice XI) and ice Ih. The intensity maps of the INS show that ice XI and ice Ih have two phonon dispersion curves in 50–65 and 72–90 meV, which assigned to the librational vibrations of water molecules. The results indicate that the phonon dispersion curves caused by the collective motions of protons exist in ice, and that ice Ih has small domains with proton-ordered arrangements. © 2003 American Institute of Physics.
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63.20.D- Phonon states and bands, normal modes, and phonon dispersion
63.20.K- Phonon interactions

Spin-exchange optical pumping of high-density xenon-129

Muhammad G. Mortuza, Satyanarayana Anala, Galina E. Pavlovskaya, Todd J. Dieken, and Thomas Meersmann

J. Chem. Phys. 118, 1581 (2003); http://dx.doi.org/10.1063/1.1539042 (4 pages) | Cited 12 times

Online Publication Date: 8 January 2003

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Gas mixtures with high xenon densities are explored for continuous flow spin-exchange optical pumping. It is shown that the 129Xe-NMR signal increases significantly with increasing xenon partial pressures up to about 200 kPa, despite a decreasing spin-polarization. Comparison of the rubidium infrared D2 emission with the xenon polarization demonstrates that radiation quenching by molecular nitrogen is of no substantial benefit for the pumping process at xenon pressures above 100 kPa. This reflects a diminished importance of spin-depolarization by radiation trapping due to the increased significance of spin-relaxation by rubidium-xenon collisions at high xenon densities. A quantitative expression for this effect is provided. © 2003 American Institute of Physics.
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32.80.Xx Level crossing and optical pumping
32.30.Dx Magnetic resonance spectra
32.50.+d Fluorescence, phosphorescence (including quenching)

A crossed molecular beams study of the O(3P)+H2 reaction: Comparison of excitation function with accurate quantum reactive scattering calculations

Donna J. Garton, Timothy K. Minton, Biswajit Maiti, Diego Troya, and George C. Schatz

J. Chem. Phys. 118, 1585 (2003); http://dx.doi.org/10.1063/1.1539043 (4 pages) | Cited 39 times

Online Publication Date: 8 January 2003

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We present the first measurements of the relative excitation function for the O(3P)+H2 reaction, performed with the use of a crossed molecular beams apparatus in conjunction with a high-energy (laser detonation) source of O atoms. The results are in excellent agreement with accurate quantum wave packet calculations. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions

Molecular dynamics simulations of microwave heating of water

Niall J. English and J. M. D. MacElroy

J. Chem. Phys. 118, 1589 (2003); http://dx.doi.org/10.1063/1.1538595 (4 pages) | Cited 21 times

Online Publication Date: 8 January 2003

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Nonequilibrium molecular dynamics simulations of water in an intense external microwave field have been performed using a rigid/polarizable and a flexible/nonpolarizable potential model, from ambient conditions to supercriticality. The heating profiles were compared to that predicted from a macroscopic energy balance, and the polarizable model was found to be superior in this regard. © 2003 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure

Arrhenius viscosity in fragile liquids due to non-Newtonian effects

Daniel J. Lacks

J. Chem. Phys. 118, 1593 (2003); http://dx.doi.org/10.1063/1.1539847 (3 pages) | Cited 3 times

Online Publication Date: 8 January 2003

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Nonequilibrium molecular dynamics simulations are carried out for a liquid undergoing shear flow. Upon cooling at constant shear rate, the temperature dependence of the viscosity changes from faster-than-Arrhenius to Arrhenius: this change is analogous to a fragile-to-strong transition. An energy landscape analysis shows that this change in the temperature dependence of the viscosity occurs because the region of the energy landscape visited by the system becomes nearly temperature-independent. © 2003 American Institute of Physics.
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66.20.-d Viscosity of liquids; diffusive momentum transport
61.20.Ja Computer simulation of liquid structure
83.50.Ax Steady shear flows, viscometric flow
47.50.-d Non-Newtonian fluid flows
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back to top Theoretical Methods and Algorithms

A path integral approach to molecular thermochemistry

Kurt R. Glaesemann and Laurence E. Fried

J. Chem. Phys. 118, 1596 (2003); http://dx.doi.org/10.1063/1.1529682 (8 pages) | Cited 5 times

Online Publication Date: 8 January 2003

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The calculation of thermochemical data requires accurate molecular energies. When such high accuracy is needed, often a method such as G1, G2, or G3 is used to calculate the energy. These methods rely upon the standard harmonic normal mode analysis to calculate the vibrational and rotational contributions to the energy. We present a method for going beyond the harmonic analysis, which uses path integral Monte Carlo to calculate the vibrational and rotational contributions. Anharmonic effects are found to be as large as 2.5 kcal/mol for the molecules studied. Analytical methods for determining an optimal path discretization are presented. A novel potential energy caching scheme, which greatly improves computational efficiency, is also presented. © 2003 American Institute of Physics.
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82.60.-s Chemical thermodynamics
71.15.Pd Molecular dynamics calculations (Car-Parrinello) and other numerical simulations
02.50.Ng Distribution theory and Monte Carlo studies

A comparison of polarized double-zeta basis sets and natural orbitals for full configuration interaction benchmarks

Micah L. Abrams and C. David Sherrill

J. Chem. Phys. 118, 1604 (2003); http://dx.doi.org/10.1063/1.1532313 (6 pages) | Cited 17 times

Online Publication Date: 8 January 2003

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We compare several standard polarized double-zeta basis sets for use in full configuration interaction benchmark computations. The 6-31G∗∗, DZP, cc-pVDZ, and Widmark–Malmqvist–Roos atomic natural orbital (ANO) basis sets are assessed on the basis of their ability to provide accurate full configuration interaction spectroscopic constants for several small molecules. Even though highly correlated methods work best with larger basis sets, predicted spectroscopic constants are in good agreement with experiment; bond lengths and harmonic vibrational frequencies have average absolute errors no larger than 0.017 Å and 1.6%, respectively, for all but the ANO basis. For the molecules considered, 6-31G∗∗ gives the smallest average errors, while the ANO basis set gives the largest. The use of variationally optimized basis sets and natural orbitals are also explored for improved benchmarking. Although optimized basis sets do not always improve predictions of molecular properties, taking a DZP-sized subset of the natural orbitals from a singles and doubles configuration interaction computation in a larger basis significantly improves results. © 2003 American Institute of Physics.
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31.15.V- Electron correlation calculations for atoms, ions and molecules
33.20.Tp Vibrational analysis
33.15.Dj Interatomic distances and angles

Full configuration interaction potential energy curves for breaking bonds to hydrogen: An assessment of single-reference correlation methods

Antara Dutta and C. David Sherrill

J. Chem. Phys. 118, 1610 (2003); http://dx.doi.org/10.1063/1.1531658 (10 pages) | Cited 45 times

Online Publication Date: 8 January 2003

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Several approximate correlation methods have been assessed for bond breaking reactions in BH, HF, and CH4 by comparison to the full configuration interaction limit. Second-order Møller–Plesset perturbation theory, coupled-cluster singles and doubles (CCSD), coupled-cluster with perturbative triples [CCSD(T)], and the hybrid density-functional method Becke three parameter Lee–Yang–Parr have been considered. Both restricted and unrestricted references have been used along with the basis sets aug-cc-pVQZ, 6-31G∗∗, and 6-31G∗ for BH, HF, and CH4 respectively. Among the methods considered, unrestricted CCSD and CCSD(T) provide potential energy curves which are the most parallel to the benchmark full CI curves, but the nonparallelity errors are fairly large (up to 6 and 4 kcal mol−1, respectively). Optimized-orbital coupled-cluster methods provide superior results but nevertheless exhibit approximately the same maximum errors. © 2003 American Institute of Physics.
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31.15.vn Electron correlation calculations for diatomic molecules
31.15.vq Electron correlation calculations for polyatomic molecules
31.50.-x Potential energy surfaces
82.30.Lp Decomposition reactions (pyrolysis, dissociation, and fragmentation)
31.15.xp Perturbation theory
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory

Linear response functions for coupled cluster/molecular mechanics including polarization interactions

Jacob Kongsted, Anders Osted, Kurt V. Mikkelsen, and Ove Christiansen

J. Chem. Phys. 118, 1620 (2003); http://dx.doi.org/10.1063/1.1529680 (14 pages) | Cited 50 times

Online Publication Date: 8 January 2003

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We present the first implementation of linear response theory for the coupled cluster/molecular mechanics (CC/MM) method. This model introduces polarization effects into a quantum mechanical/molecular mechanical (QM/MM) framework using a self-consistent procedure while electrostatic effects are modeled by assigning partial charges to the MM molecules and a van der Waals potential describes dispersion and short range repulsion. The quantum mechanical subsystem is described using coupled cluster electronic structure methods. The response theory for the calculation of molecular properties for such a model is described and implemented at the coupled cluster singles and doubles (CCSD) level. Sample calculations of excitation energies, transition moments and frequency dependent polarizabilities for liquid water are presented. Finally, we consider the development of a parameter independent iterative self-consistent CC/MM model where the properties calculated by CC/MM response theory are used in the QM/MM interaction Hamiltonian. © 2003 American Institute of Physics.
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61.20.Ja Computer simulation of liquid structure
61.20.Ne Structure of simple liquids
02.70.Ns Molecular dynamics and particle methods
31.15.bw Coupled-cluster theory

A mode-selective quantum chemical method for tracking molecular vibrations applied to functionalized carbon nanotubes

Markus Reiher and Johannes Neugebauer

J. Chem. Phys. 118, 1634 (2003); http://dx.doi.org/10.1063/1.1523908 (8 pages) | Cited 27 times

Online Publication Date: 8 January 2003

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The theoretical investigation of mesoscopic objects requires new techniques which are particularly suited for the study of selected aspects of these systems. Vibrational spectroscopy is a main source for structural information on heterogeneous systems. We present an efficient quantum chemical method, which relies on a modified Davidson algorithm for targeting selected vibrations in infrared and Raman spectra. This approach is applied to the characteristic breathing modes of single-walled carbon nanotubes. © 2003 American Institute of Physics.
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33.20.Tp Vibrational analysis
31.15.E- Density-functional theory
31.15.bu Semi-empirical and empirical calculations (differential overlap, Hückel, PPP methods, etc.)
36.40.-c Atomic and molecular clusters
back to top Gas Phase Dynamics and Structure: Spectroscopy, Molecular Interactions, Scattering, and Photochemistry

Discovery of the optically forbidden S1–S0 transition of silylidene (H2C�Si)

Tony C. Smith, Corey J. Evans, and Dennis J. Clouthier

J. Chem. Phys. 118, 1642 (2003); http://dx.doi.org/10.1063/1.1531618 (7 pages) | Cited 3 times

Online Publication Date: 8 January 2003

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The electronically forbidden  1A2–math 1A1 band system of jet-cooled silylidene (H2CSi and D2CSi) has been detected for the first time using laser-induced fluorescence (LIF) and stimulated emission pumping (SEP) techniques. The very weak, vibronically induced 401 and 301401 bands were detected by LIF along with the corresponding 601 and 301601 bands which gain intensity through excited state Coriolis coupling. SEP spectra, obtained by pumping the 000 band of the S2 state and stimulating transitions down to the S1 state through the allowed S2–S1 transition, revealed many more bands, including the 000 bands, which were studied at high resolution and rotationally analyzed. From the upper state rotational constants of H2CSi and D2CSi, the excited state structure was obtained as r0′ (SiC) = 1.873(2) Å, r0′(CH) = 1.099(5) Å, and θ0′(HCH) = 113.9(3)°. The four lowest energy excited state vibrational frequencies of both isotopomers have also been determined. High level ab initio predictions of the ground and excited state properties of silylidene are also reported and found to be in good agreement with the experimentally determined values. © 2003 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.80.Be Level crossing and optical pumping
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
33.70.Fd Absolute and relative line and band intensities
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Sn Rotational analysis
33.20.Tp Vibrational analysis
31.30.Gs Hyperfine interactions and isotope effects
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Rotational spectrum, dynamics, and bond energy of the floppy dimethylether⋯neon van der Waals complex

Assimo Maris and Walther Caminati

J. Chem. Phys. 118, 1649 (2003); http://dx.doi.org/10.1063/1.1533012 (4 pages) | Cited 11 times

Online Publication Date: 8 January 2003

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The equilibrium conformation, dynamics, and dissociation energy of the weakly bonded dimethylether⋯Ne complex have been deduced from its pulsed jet millimeter wave spectrum. Each rotational transition is split into two component lines. The corresponding vibrational splitting has been determined to be ΔE = 807.2(9) MHz. The inversion barrier between the two equivalent minima with Ne above or below the COC plane has been calculated from this datum to be 16 cm−1. The dissociation energy of the complex is estimated, from the centrifugal distortion constant DJ, to be ca. 1.0 kJ/mol. © 2003 American Institute of Physics.
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33.20.Bx Radio-frequency and microwave spectra
33.20.Sn Rotational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.15.Bh General molecular conformation and symmetry; stereochemistry
33.15.Fm Bond strengths, dissociation energies
33.20.Tp Vibrational analysis

Ab initio potential energy surface for vibrational state calculations of H2CO

Kiyoshi Yagi, Chikako Oyanagi, Tetsuya Taketsugu, and Kimihiko Hirao

J. Chem. Phys. 118, 1653 (2003); http://dx.doi.org/10.1063/1.1531105 (8 pages) | Cited 25 times

Online Publication Date: 8 January 2003

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A highly accurate potential energy function for H2CO has been developed at the CCSD(T)/cc-pVTZ level. The potential energy function is generated by the modified Shepard interpolation of the local fourth-order Taylor expansions defined at three reference points, i.e., the equilibrium structure plus two symmetrically equivalent structures located in the strongly coupled region of CH symmetric (Q1) and antisymmetric (Q5) stretching vibrational coordinates. The vibrational self-consistent field and the following vibrational configuration interaction methods have been applied to determine the fundamentals, overtones, and combination bands of H2CO. It is shown that our proposed potential energy function and a conventional quartic force field provide the different result related to the assignment of the 1151 and 113161 bands. The calculated vibrational energies are in good agreement with the corresponding experimental values, showing the mean absolute deviation of 7.7 cm−1. © 2003 American Institute of Physics.
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31.15.A- Ab initio calculations
31.50.-x Potential energy surfaces
33.15.Mt Rotation, vibration, and vibration-rotation constants
31.15.xr Self-consistent-field methods
31.15.vq Electron correlation calculations for polyatomic molecules

Temperature dependence of the collisional energy transfer of OH(v = 10) between 220 and 310 K

Jean Lacoursière, Mark J. Dyer, and Richard A. Copeland

J. Chem. Phys. 118, 1661 (2003); http://dx.doi.org/10.1063/1.1530581 (6 pages) | Cited 9 times

Online Publication Date: 8 January 2003

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The temperature dependence of the thermally averaged collisional removal cross section of OH (X 2∏, v = 10) by O2, N2O, and CO2 is measured between 220 and 310 K using a two-laser pump–probe technique and a specially designed vacuum-isolated flow cell. OH molecules are generated in v = 6–9 by the reaction of hydrogen atoms and ozone. The (10,7) vibrational transition is excited with pulsed near-infrared laser light to create a population of OH (v = 10) molecules. The temporal evolution of the v = 10 population is monitored as a function of collider gas pressure by a time-delayed ultraviolet laser pulse. The probe step uses laser-induced fluorescence by exciting the B 2∑+–X 2∏ (0,10) transition and detecting the fluorescence from the B 2∑+–A 2∑+ (0,6–8) transitions. From 310 to 223 K, the OH (v = 10) removal cross section increases by 35±21, 33±14, and 58±48 percent for the colliders O2, N2O, and CO2, respectively. This inverse temperature dependence is typical of a loss mechanism governed by long-range attractive forces. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
33.50.Dq Fluorescence and phosphorescence spectra

The H2–H complex: Interaction-induced dipole surface and infrared absorption spectra

Magnus Gustafsson, Lothar Frommhold, and Wilfried Meyer

J. Chem. Phys. 118, 1667 (2003); http://dx.doi.org/10.1063/1.1529681 (6 pages) | Cited 3 times

Online Publication Date: 8 January 2003

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A quantum chemical dipole surface of interacting H2–H pairs is obtained and collision-induced absorption spectra are computed for temperatures from 200 to 1000 K and frequencies from 0 to 6000 cm−1. The effect of the anisotropy of the potential energy is investigated and turns out to be almost negligible at the temperature for which a close-coupled quantum calculation was done. The smallness of the effect stems from the short range character of the anisotropic potential components for H2–H. Accordingly the isotropic potential approximation could be applied in most of the present calculations. The accuracy of the dipole surface as well as that of the ab initio potential energy surface that enters the calculations of the spectra are believed to permit prediction of absolute spectral intensities with an accuracy in the 5% range. © 2003 American Institute of Physics.
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33.20.Ea Infrared spectra
31.50.-x Potential energy surfaces
31.15.A- Ab initio calculations
33.70.Fd Absolute and relative line and band intensities

A theoretical study of cis–trans isomerization in HONO using an empirical valence bond potential

Yin Guo and Donald L. Thompson

J. Chem. Phys. 118, 1673 (2003); http://dx.doi.org/10.1063/1.1530585 (6 pages) | Cited 18 times

Online Publication Date: 8 January 2003

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The empirical valence bond (EVB) approach proposed by Chang and Miller [J. Phys. Chem. 94, 5884 (1990)] for constructing global potential energy surfaces has the potential for treating large molecular systems. In this work, we slightly modify the expression of Chang and Miller by adding a damping function along the reaction coordinate to ensure the proper asymptotic behavior of the potential. We apply the EVB method to describe the cis–trans isomerization in HONO, and compute the isomerization rates in the low-energy tunneling regime by employing the semiclassical method that treats tunneling within classical trajectory calculations. © 2003 American Institute of Physics.
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82.30.Qt Isomerization and rearrangement
31.15.xw Valence bond calculations
31.50.-x Potential energy surfaces

Time delays in cold elastic scattering

David Field and Lars Bojer Madsen

J. Chem. Phys. 118, 1679 (2003); http://dx.doi.org/10.1063/1.1530584 (5 pages) | Cited 12 times

Online Publication Date: 8 January 2003

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Expressions are derived for time delays for elastic scattering in cold electron and cold atom collisions. Delays are found to occur in the femtosecond regime for virtual state electron scattering with CO2, using recent experimental data [Field et al., Phys. Rev. A 64, 22708 (2001)]. Delays associated with cold atom scattering may be of the order of 1 μs in the μK regime, using 6Li collisions as an example. The maximum theoretical time delay, obtained by magnetically tuning the scattering length, is found to have a universal value at any ultracold collision energy E, given by (2E)−1. © 2003 American Institute of Physics.
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34.80.Bm Elastic scattering

Solvated electron in (H2O)20− and (H2O)21− clusters: A theoretical study

Arshad Khan

J. Chem. Phys. 118, 1684 (2003); http://dx.doi.org/10.1063/1.1531100 (4 pages) | Cited 22 times

Online Publication Date: 8 January 2003

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The dodecahedral (H2O)20− and (H2O)21− clusters are studied by applying the Becke-3-parameter density functional theory and Lee–Yang–Parr correlation functional. The geometry optimizations are carried out with 6-31G∗ basis set followed by single-point calculations for energy and charge distribution values with 6-311++G∗∗ basis set. While the structures of these clusters are very similar to their neutral counterparts, the charge distributions are significantly different. In the dodecahedral (H2O)20− cluster with an empty cavity, the −1 charge is distributed almost evenly among the half of the water molecules (10) on the cage surface. However, in a filled dodecahedral (H2O)21− cluster, the −1 charge is almost entirely localized unto the water molecule in the cavity. The calculated electron binding energies for the (H2O)20− and (H2O)21− clusters are 0.805 and 1.12 eV, respectively, and the stabilization energies relative to monomers and separated electron are 202 and 214 kcal/mol, respectively. © 2003 American Institute of Physics.
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36.40.Wa Charged clusters
31.15.E- Density-functional theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Mechanisms for the ozonolysis of ethene and propene: Reliability of quantum chemical predictions

Wai-To Chan and I. P. Hamilton

J. Chem. Phys. 118, 1688 (2003); http://dx.doi.org/10.1063/1.1531104 (14 pages) | Cited 13 times

Online Publication Date: 8 January 2003

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Reactions of ozone with ethene and propene leading to primary ozonide (concerted and stepwise ozonolysis) or epoxide and singlet molecular oxygen (partial ozonolysis) are studied theoretically. The mechanism of concerted ozonolysis proceeds via a single transition structure which is a partial diradical. The transition structures and intermediates in the stepwise ozonolysis and partial ozonolysis mechanisms are singlet diradicals. Spin-restricted and unrestricted density functional methods are employed to calculate the structures of the closed-shell and diradical species. Although the partial diradicals exhibit moderate to pronounced instability in their RDFT and RHF solutions, RDFT is required to locate the transition structure for concerted ozonolysis. Spin projected fourth-order Møller–Plesset theory (PMP4) was used to correct the DFT energies. The calculated pre-exponential factors and activation energies for the concerted ozonolysis of ethene and propene are in good agreement with experimental values. However, the PMP4//DFT procedure incorrectly predicts the stepwise mechanism as the favored channel. UCCSD(T) predicts the concerted mechanism as the favored channel but significantly overestimates the activation energies. RCCSD(T) is found to be more accurate than UCCSD(T) for the calculation of the concerted mechanism but is not applicable to the diradical intermediates. The major difficulty in accurate prediction of the rate constant data for these reactions is the wide range of spin contamination for the reference UHF wave functions and UDFT solutions across the potential energy surface. The possibility of the partial ozonolysis mechanism being the source of epoxide observed in some experiments is discussed. © 2003 American Institute of Physics.
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
31.15.bw Coupled-cluster theory
31.15.E- Density-functional theory
31.15.xp Perturbation theory

The valence-excited states T1–T4 and S1–S2 of acetylene: A high-level MR-CISD and MR-AQCC investigation of stationary points, potential energy surfaces, and surface crossings

Elizete Ventura, Michal Dallos, and Hans Lischka

J. Chem. Phys. 118, 1702 (2003); http://dx.doi.org/10.1063/1.1532312 (12 pages) | Cited 18 times

Online Publication Date: 8 January 2003

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Valence-excited singlet (S1,S2) and triplet (T1–T4) states of acetylene have been studied by means of extended multireference electron correlation techniques (MR-CISD, MR-CISD+Q, and MR-AQCC). Extrapolations to the basis set limit have been performed. Minima and saddle points have been calculated using a recently developed analytic gradient method for excited states. Planar as well as nonplanar structures have been considered. In particular, the existence of an asymmetric, planar cis-type minimum on the S2 surface has been confirmed conclusively. Moreover, an intersection S1/S2 has been located close to this minimum. This situation will most probably affect the interpretation of the absorption bands attributed to the trans 1 1Bu state. In-plane and out-of-plane saddle points for cis–trans isomerization have been determined and characterized by harmonic vibrational analysis. Several interesting surface crossings for different electronic states (S1/S2, T2/T3, and S1/T3) have been characterized. Implications of the flatness of the T3 surface around linear structures and the location of the S1/T3 crossing seam on the anomalities observed in the ZAC spectrum of the  1Au state are discussed. © 2003 American Institute of Physics.
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31.50.Df Potential energy surfaces for excited electronic states
31.15.vq Electron correlation calculations for polyatomic molecules
82.30.Qt Isomerization and rearrangement

Multireference configuration interaction calculations of some low-lying states of positronium hydride

Shiro L. Saito

J. Chem. Phys. 118, 1714 (2003); http://dx.doi.org/10.1063/1.1531101 (7 pages) | Cited 9 times

Online Publication Date: 8 January 2003

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Multireference configuration interaction (MRCI) calculations of the ground state 2,1S and low-lying excited states 2,1P, 2,1D, and 2,3S of positronium hydride (PsH) were carried out, and their total energies and two-photon annihilation rates were presented. Our MRCI calculations gave more compact and accurate wave functions than recent large scale full CI ones, and the effectiveness of the MRCI method for positron-atom complexes was shown. Two extrapolation methods derived from an analysis of the convergence pattern of the total energies and two-photon annihilation rates with respect to angular momentum of orbitals were attempted in order to estimate full CI limit of those values. As a result, our reliable extrapolation method gave −0.788 642, −0.732 826, −0.724 642, and −0.739 829 a.u. for the total energies of the 2,1S, 2,1P, 2,1D, and 2,3S states of PsH, respectively. For the two-photon annihilation rates of the respective states, 2.1078, 1.5702, 1.0980, and 1.0784 ns−1 were obtained, respectively. © 2003 American Institute of Physics.
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36.10.Dr Positronium
31.15.vn Electron correlation calculations for diatomic molecules
33.80.-b Photon interactions with molecules
02.60.-x Numerical approximation and analysis

Molecular structure, vibrational frequencies, energetics, and excited states of the HOONO+ ions

John D. Watts and Joseph S. Francisco

J. Chem. Phys. 118, 1721 (2003); http://dx.doi.org/10.1063/1.1531661 (8 pages) | Cited 1 time

Online Publication Date: 8 January 2003

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Equilibrium geometries have been optimized and harmonic vibrational frequencies obtained for neutral HOONO and its cation employing quadratic configuration interaction methods and correlation-consistent basis sets. The lowest energy structure of HOONO+ found is a planar conformer on the 2A′ potential-energy surface with a cis–trans arrangement [τ(OONO) = 0° and τ(HOON) = 180°]. This is quite the opposite from neutral HOONO, which prefers a cis–cis arrangement because of hydrogen bonding. The adiabatic ionization potential for HOONO is predicted to be 260.0±1 kcal mol−1 (11.3 eV) at the complete basis set limit. A planar ion–molecule complex formed from HO2 and NO+ was located on the 2A″ surface. The binding energy of this complex relative to HO2 and NO+ is estimated to be 18.1±1 kcal mol−1 at the complete basis set limit. Excited states of the HOONO+ ion were also calculated with quasi-restricted Hartree–Fock and unrestricted Hartree–Fock coupled-cluster methods including connected triple excitations. © 2003 American Institute of Physics.
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33.15.Bh General molecular conformation and symmetry; stereochemistry
33.20.Tp Vibrational analysis
31.15.vq Electron correlation calculations for polyatomic molecules
33.15.Fm Bond strengths, dissociation energies
31.15.xr Self-consistent-field methods
31.15.bw Coupled-cluster theory
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Untrapped dynamics of molecules within an accelerating optical lattice

Guangjiong Dong, Weiping Lu, and P. F. Barker

J. Chem. Phys. 118, 1729 (2003); http://dx.doi.org/10.1063/1.1533079 (6 pages) | Cited 4 times

Online Publication Date: 8 January 2003

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We investigate the dynamics of untrapped molecules within a far-off resonant accelerating optical lattice. Our analysis shows that untrapped molecules can be temporarily transported by the lattice, and those that are transported for the longest time reach a unique, well-defined critical velocity that depends on the mass to polarizability ratio of the molecular species. We show that this species-dependent critical velocity leads to a velocity dispersion for different species within a gas mixture. Our numerical simulations show that the velocity distribution of a multicomponent gas evolves to form well-separated peaks in velocity space for each species. We propose a time-of-flight analysis technique that transforms the velocity dispersion to a temporal separation of different species, even for small differences in the mass to polarizability ratio. Separation utilizing this concept is demonstrated for atmospheric species and isotopes of nitrogen. Finally, we present an extension of this concept for both temporal and angular dispersion. © 2003 American Institute of Physics.
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37.10.Mn Slowing and cooling of molecules
37.10.Pq Trapping of molecules
33.15.Kr Electric and magnetic moments (and derivatives), polarizability, and magnetic susceptibility

Theoretical modeling of the OH stretch infrared spectrum of carboxylic acid dimers based on first-principles anharmonic couplings

Gina M. Florio, Timothy S. Zwier, Evgeniy M. Myshakin, Kenneth D. Jordan, and Edwin L. Sibert

J. Chem. Phys. 118, 1735 (2003); http://dx.doi.org/10.1063/1.1530573 (12 pages) | Cited 59 times

Online Publication Date: 8 January 2003

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Carboxylic acid dimers serve as prototypical systems for modeling the unusual spectral behavior of the hydride stretch fundamental. Large anharmonic effects associated with the pair of cooperatively strengthened OH⋯O�C hydrogen bonds produces complicated infrared spectra in which the OH stretch oscillator strength is spread over hundreds of wave numbers, resulting in a complicated band sub-structure. In this work cubic anharmonic constants are computed along internal coordinates associated with the intramolecular OH stretch, intermolecular stretch, and OH bend internal coordinates for the formic acid and benzoic acid dimers. These are then projected onto the normal coordinates to produce mixed states that are used in computing the OH stretch infrared spectrum. For the benzoic acid dimer the calculations accurately reproduce for three deuterated isotopomers the overall breadth and much of the vibrational sub-structure in the observed spectra. For the formic acid dimer, the spectrum is calculated using a model employing a subset of the cubic force constants as well as using the full cubic force field. The spectra calculated for the formic acid dimer are sparser and somewhat more sensitive to the exact positions of the anharmonically coupled states than that of the benzoic acid dimer. Again semiquantitative agreement with experiment is obtained. © 2003 American Institute of Physics.
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33.20.Ea Infrared spectra
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)
34.20.Gj Intermolecular and atom-molecule potentials and forces

Electronic structure of isolated PtX62− (X = F,Cl,Br) dianions

Thomas Sommerfeld, Sven Feuerbacher, Markus Pernpointner, and Lorenz S. Cederbaum

J. Chem. Phys. 118, 1747 (2003); http://dx.doi.org/10.1063/1.1529678 (9 pages) | Cited 11 times

Online Publication Date: 8 January 2003

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The dianions PtCl62− and PtBr62− belong to the small class of doubly charged species whose gas phase photoelectron spectra have been measured and show clearly discernible structures. Here we study the electronic structure of the PtX62− (X = F,Cl,Br) dianions and the associated electron detachment energies theoretically. Relativistic effects including spin–orbit splittings are investigated at the self consistent field level by comparing nonrelativistic all-electron computations with results obtained using the Douglas–Kroll and the Dirac–Fock Hamiltonians as well as relativistic effective core potentials. Electron correlation effects, which are known to substantially influence detachment energies of mono- and dianionic species, are addressed at the configuration interaction and two propagator based levels of theory employing the relativistic effective core potentials. Moreover, we study the repulsive Coulomb barriers of the PtX62− systems within the dianion frozen orbital static approximation. Our findings strongly disagree with the standard textbook molecular orbital diagram of coordination compounds as well as with the tentative assignment of the spectroscopists. In particular, the five highest orbitals of PtCl62− and PtBr62− exhibit almost exclusively ligand character. The theoretical results are explained in terms of the charge distribution within the gas phase dianions, and the impact on assigning the photoelectron spectrum is discussed. © 2003 American Institute of Physics.
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31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.A- Ab initio calculations
31.15.vj Electron correlation calculations for atoms and ions: excited states
33.80.Eh Autoionization, photoionization, and photodetachment
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