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22 Apr 1999

Volume 110, Issue 16, pp. 7607-8206

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Characterization of the I3 radical by anion photoelectron spectroscopy

Travis R. Taylor, Knut R. Asmis, Martin T. Zanni, and Daniel M. Neumark

J. Chem. Phys. 110, 7607 (1999); http://dx.doi.org/10.1063/1.478672 (3 pages) | Cited 14 times

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The ground and first excited states of the I3 radical are characterized by photoelectron spectroscopy of I3− and Ar⋅I3− at 266 nm. The electron affinity of I3 is 4.226±0.013 eV. Based on the recently determined bond dissociation energy of I3−, the I3 ground state is bound by 0.143±0.06 eV. The first excited state of I3 lies 0.27 eV above the ground state. A vibrational progression is seen in the ground state band of the I3− photoelectron spectrum. The addition of an argon atom to I3− reduces the contribution of hot bands to the photoelectron spectrum, facilitating the interpretation of the vibrational structure. Simulations indicate that the I3 ground state is linear with a symmetric stretch frequency of 115±5 cm−1 and is likely to be centrosymmetric. © 1999 American Institute of Physics.
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33.60.+q Photoelectron spectra
31.50.Df Potential energy surfaces for excited electronic states
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy
33.15.Fm Bond strengths, dissociation energies
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
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Jastrow corrected time-dependent self-consistent field approximation

Joshua Wilkie, Mark A. Ratner, and R. B. Gerber

J. Chem. Phys. 110, 7610 (1999); http://dx.doi.org/10.1063/1.478673 (12 pages) | Cited 8 times

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An improved approximation to the time-dependent Schrödinger equation is developed by correcting the time-dependent self-consistent field ansatz with a Jastrow prefactor defined via a set of variationally determined time-dependent parameters and a linearly independent set of prespecified spatial functions. The method is applicable in any number of dimensions, conserves norm and energy, is without parametric singularities, possesses an internal estimate of the accuracy, and has computational costs that scale algebraically with the number of degrees of freedom. The new formalism is applied to a two-dimensional double well potential to demonstrate the improved accuracy of the method. An extension of the method to electronically nonadiabatic problems is also presented. © 1999 American Institute of Physics.
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31.15.xr Self-consistent-field methods
03.65.Ge Solutions of wave equations: bound states
33.15.Hp Barrier heights (internal rotation, inversion, rotational isomerism, conformational dynamics)

Uniform J-shifting approach for calculating reaction rate constant

D. H. Zhang and J. Z. H. Zhang

J. Chem. Phys. 110, 7622 (1999); http://dx.doi.org/10.1063/1.478802 (5 pages) | Cited 30 times

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This paper presents a new uniform J-shifting approach for accurate calculation of rate constant in quantum dynamics study of chemical reaction. Instead of using a fixed shifting constant B in the standard J-shifting approach, the current method employs a temperature-dependent shifting constant which is obtained through an optimization procedure at a given temperature. By utilizing the calculated reaction probabilities at only a few total angular momentum values of J, the current approach automatically gives uniformly accurate rate constant across the entire range of temperature. Numerical studies of several benchmark reaction systems, including the H+H2, H2+OH and H2+CN reactions, show explicitly that the uniform J-shifting approach is far superior to the standard J-shifting approach and it provides a robust method for accurate and efficient calculation of reaction rate constant in rigorous quantum dynamics study of chemical reaction. © 1999 American Institute of Physics.  
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82.20.Pm Rate constants, reaction cross sections, and activation energies
02.60.Pn Numerical optimization

Nuclear magnetic shieldings in solution: Gauge invariant atomic orbital calculation using the polarizable continuum model

Roberto Cammi, Benedetta Mennucci, and Jacopo Tomasi

J. Chem. Phys. 110, 7627 (1999); http://dx.doi.org/10.1063/1.478674 (12 pages) | Cited 32 times

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We present the gauge invariant atomic orbital (GIAO) calculation of nuclear magnetic shieldings for solvated molecules described within the polarizable continuum model (PCM). The performance of the PCM-GIAO approach is tested in a benchmark calculation of isotropic 13C, 15N, and 17O shielding constants for CH3CN and CH3NO2 in vacuo and in water, both at the Hartree–Fock and density functional levels of theory. Various aspects of the calculation of solvent effects on these properties, such as the dependence on the basis set, the electron correlation, and the size of the molecular cavity embedding the solute, are taken into account and discussed. An interpretation of the gas-to-solution shielding variations in terms of a combined action of the solvent reaction field and the shielding polarizabilities is also given. © 1999 American Institute of Physics.
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31.30.-i Corrections to electronic structure
31.15.xr Self-consistent-field methods
31.15.E- Density-functional theory
31.15.vq Electron correlation calculations for polyatomic molecules

Diffusion-assisted long-range reactions in confined systems: Projection operator approach

Kazuhiko Seki, Alexander V. Barzykin, and M. Tachiya

J. Chem. Phys. 110, 7639 (1999); http://dx.doi.org/10.1063/1.478675 (11 pages) | Cited 24 times

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The diffusion-assisted long-range reversible reaction equation is solved for the pair survival probability using a projection operator method in terms of the diffusion propagator in the absence of reaction. For a localized (delta function) reaction sink, the well-known analytical solution is immediately reproduced from the operator expression. It is emphasized that the mean reaction time approach, often used to approximate the overall reaction rate, is not adequate for a nonequilibrium initial condition. The general operator solution for a delocalized sink is shown to reduce to a closed matrix form, provided the propagator has a discrete spectrum of eigenmodes. The matrix solution is exact and applies for an arbitrary functional form and strength of the reaction sink. Although matrices of infinite dimensions are involved, they can be truncated at a certain finite dimension to attain any prescribed precision. Convergence of the truncated matrix solution is fast and often only a few of the lowest eigenmodes are sufficient to obtain quantitatively reasonable results. Several long-range reaction models are analyzed in detail revealing the breakdown of the widely used closure approximation obtained as a first-order Padé approximation of the operator solution. © 1999 American Institute of Physics.
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82.20.-w Chemical kinetics and dynamics
02.60.-x Numerical approximation and analysis

Gaussian-3 theory using density functional geometries and zero-point energies

Anwar G. Baboul, Larry A. Curtiss, Paul C. Redfern, and Krishnan Raghavachari

J. Chem. Phys. 110, 7650 (1999); http://dx.doi.org/10.1063/1.478676 (8 pages) | Cited 432 times

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A variation of Gaussian-3 (G3) theory is presented in which the geometries and zero-point energies are obtained from B3LYP density functional theory [B3LYP/6-31G(d)] instead of geometries from second-order perturbation theory [MP2(FU)/6-31G(d)] and zero-point energies from Hartree–Fock theory [HF/6-31G(d)]. This variation, referred to as G3//B3LYP, is assessed on 299 energies (enthalpies of formation, ionization potentials, electron affinities, proton affinities) from the G2/97 test set [J. Chem. Phys. 109, 42 (1998)]. The G3//B3LYP average absolute deviation from experiment for the 299 energies is 0.99 kcal/mol compared to 1.01 kcal/mol for G3 theory. Generally, the results from the two methods are similar, with some exceptions. G3//B3LYP theory gives significantly improved results for several cases for which MP2 theory is deficient for optimized geometries, such as CN and O2+. However, G3//B3LYP does poorly for ionization potentials that involve a Jahn–Teller distortion in the cation (CH4+, BF3+, BCl3+) because of the B3LYP/6-31G(d) geometries. The G3(MP2) method is also modified to use B3LYP/6-31G(d) geometries and zero-point energies. This variation, referred to as G3(MP2)//B3LYP, has an average absolute deviation of 1.25 kcal/mol compared to 1.30 kcal/mol for G3(MP2) theory. Thus, use of density functional geometries and zero-point energies in G3 and G3(MP2) theories is a useful alternative to MP2 geometries and HF zero-point energies. © 1999 American Institute of Physics.
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31.15.E- Density-functional theory
31.15.xp Perturbation theory
31.15.xr Self-consistent-field methods
82.60.Cx Enthalpies of combustion, reaction, and formation
32.50.+d Fluorescence, phosphorescence (including quenching)
33.15.Ry Ionization potentials, electron affinities, molecular core binding energy

Coherent stabilization of zero-electron-kinetic-energy states

Paolo Bellomo and C. R. Stroud

J. Chem. Phys. 110, 7658 (1999); http://dx.doi.org/10.1063/1.478677 (9 pages) | Cited 6 times

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The accuracy of zero-electron-kinetic-energy (ZEKE) photoelectron spectroscopy rests on the ultralong lifetimes of the high-n, high-l Rydberg states that are responsible for the ZEKE signal. However, a few-photon process cannot excite electrons directly from the low-l ground state to the high-l ZEKE manifold. In this paper we show that using the dynamics of Rydberg Stark states in slowly time dependent external fields it is possible to control coherently the angular momentum of Rydberg electrons, and therefore also their lifetime. We derive explicitly two different schemes based on simple, short electric dc pulses, which populate precisely those high-l, long-lived Rydberg states that are necessary for accurate ZEKE experiments. The high-l states that we construct are also Stark eigenstates, therefore a moderate dc external field can eventually enforce cylindrical symmetry and lock the ZEKE electrons in the stable, long-lived high-l manifold. © 1999 American Institute of Physics.
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32.80.Fb Photoionization of atoms and ions
33.60.+q Photoelectron spectra
32.60.+i Zeeman and Stark effects
33.57.+c Magneto-optical and electro-optical spectra and effects

Gaussian basis sets for use in correlated molecular calculations. IX. The atoms gallium through krypton

Angela K. Wilson, David E. Woon, Kirk A. Peterson, and Thom H. Dunning

J. Chem. Phys. 110, 7667 (1999); http://dx.doi.org/10.1063/1.478678 (10 pages) | Cited 323 times

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Valence correlation consistent and augmented correlation consistent basis sets have been determined for the third row, main group atoms gallium through krypton. The methodology, originally developed for the first row atoms, was first applied to the selenium atom, resulting in the expected natural groupings of correlation functions (although higher angular momentum functions tend to be relatively more important for the third row atoms as they were for the second row atoms). After testing the generality of the conclusions for the gallium atom, the procedure was used to generate correlation consistent basis sets for all of the atoms gallium through krypton. The correlation consistent basis sets for the third row main group atoms are as follows: cc-pVDZ: (14s11p6d)/[5s4p2d]; cc-pVTZ: (20s13p9d1f )/[6s5p3d1f]; cc-pVQZ: (21s16p12d2 f1g)/[7s6p4d2 f1g]; cc-pV5Z: (26s17p13d3f2g1h)/[8s7p5d3f2g1h]. Augmented sets were obtained by adding diffuse functions to the above sets (one for each angular momentum present in the set), with the exponents of the additional functions optimized in calculations on the atomic anions. Test calculations on the atoms as well as selected molecules with the new basis sets show good convergence to an apparent complete basis set limit. © 1999 American Institute of Physics.
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31.15.-p Calculations and mathematical techniques in atomic and molecular physics

Electronic-structure calculations by first-principles density-based embedding of explicitly correlated systems

Niranjan Govind, Yan Alexander Wang, and Emily A. Carter

J. Chem. Phys. 110, 7677 (1999); http://dx.doi.org/10.1063/1.478679 (12 pages) | Cited 72 times

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A first-principles embedding theory that combines the salient features of density functional theory (DFT) and traditional quantum chemical methods is presented. The method involves constructing a DFT-based embedding potential and then using it as a one-electron operator within a very accurate ab initio calculation. We demonstrate how DFT calculations can be systematically improved via this procedure. The scheme is tested using two closed shell systems, a toy model Li2Mg2, and the experimentally well characterized CO/Cu(111) system. Our results are in good agreement with near full configuration interaction calculations in the former case and experimental adsorbate binding energies in the latter. This method provides the means to systematically include electron correlation in a local region of a condensed phase. © 1999 American Institute of Physics.
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31.15.E- Density-functional theory
31.15.A- Ab initio calculations
68.08.-p Liquid-solid interfaces
68.43.-h Chemisorption/physisorption: adsorbates on surfaces

Density functional calculations of nuclear magnetic shieldings using the zeroth-order regular approximation (ZORA) for relativistic effects: ZORA nuclear magnetic resonance

S. K. Wolff, T. Ziegler, E. van Lenthe, and E. J. Baerends

J. Chem. Phys. 110, 7689 (1999); http://dx.doi.org/10.1063/1.478680 (10 pages) | Cited 117 times

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We present a new relativistic formulation for the calculation of nuclear magnetic resonance (NMR) shielding tensors. The formulation makes use of gauge-including atomic orbitals and is based on density functional theory. The relativistic effects are included by making use of the zeroth-order regular approximation. This formulation has been implemented and the 199Hg NMR shifts of HgMe2, HgMeCN, Hg(CN)2, HgMeCl, HgMeBr, HgMeI, HgCl2, HgBr2, and HgI2 have been calculated using both experimental and optimized geometries. For experimental geometries, good qualitative agreement with experiment is obtained. Quantitatively, the calculated results deviate from experiment on average by 163 ppm, which is approximately 3% of the range of 199Hg NMR. The experimental effects of an electron donating solvent on the mercury shifts have been reproduced with calculations on HgCl2(NH3)2, HgBr2(NH3)2, and HgI2(NH3)2. In addition, it is shown that the mercury NMR shieldings are sensitive to geometry with changes for HgCl2 of approximately 50 ppm for each 0.01 Å  change in bond length, and 100 ppm for each 10° change in bond angle. © 1999 American Institute of Physics.
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33.25.+k Nuclear resonance and relaxation
31.30.J- Relativistic and quantum electrodynamic (QED) effects in atoms, molecules, and ions
31.15.E- Density-functional theory
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The A 3Π state of SO

John M. F. Elks and Colin M. Western

J. Chem. Phys. 110, 7699 (1999); http://dx.doi.org/10.1063/1.478681 (8 pages) | Cited 11 times

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Laser induced fluorescence and 1+1 resonance enhanced multiphoton ionisation spectra of the A 3Π–X 3Σ− transition of SO radicals prepared by an electric discharge in a supersonic jet expansion are presented. Rotational constants are given for A state vibrational levels with v′ = 0–13, extending to within 190 cm−1 of the A state dissociation limit. The Rydberg–Klein–Rees curve derived from these constants shows significant anharmonicity, even around the equilibrium geometry. In addition, several small local perturbations of the rotational structure are observed. Collision free fluorescence lifetimes are determined for the complete range of vibrational states, and are found to fall smoothly from 29.5 μs for v′ = 0 to 6.45 μs for v′ = 12. Combining these data with earlier measurements leads to a better determination of the A–X transition dipole moment over the range 1.4–2.0 Å. © 1999 American Institute of Physics.
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33.50.Dq Fluorescence and phosphorescence spectra
33.80.Eh Autoionization, photoionization, and photodetachment
33.80.Wz Other multiphoton processes
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
33.70.Ca Oscillator and band strengths, lifetimes, transition moments, and Franck-Condon factors

Stereodynamics of the vibrational channel O(1D)+H2O→OH(v′ = 2)+OH

Hiroshi Tsurumaki, Yo Fujimura, and Okitsugu Kajimoto

J. Chem. Phys. 110, 7707 (1999); http://dx.doi.org/10.1063/1.478682 (10 pages) | Cited 9 times

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The state-selected differential cross section (DCS) and rotational angular momentum polarization for the reaction O(1D)+H2O→OH+OH have been measured by utilizing the polarized Doppler-resolved laser-induced fluorescence probing technique. Stereodynamics of the reaction channel forming the newly formed OH in the specific vibrational level v′ = 2 is discussed on the basis of the vector properties. A nearly isotropic DCS for the product OH(2Π3/2, v′ = 2, j′ = 5.5) most probably indicates that the reaction is dominated by an insertion mechanism involving a collisional HOOH complex with a lifetime comparable to its rotational period. The extremely asymmetrical energy partitioning between the two OH fragments, therefore, suggests that the redistribution of the available energy does not occur on a time scale comparable to the rotational period of the complex. Furthermore, it has been found that the product rotational angular momentum vector j′ is predominantly perpendicular to the collision plane spanned by k and k′ (the relative velocity vectors of the reactants and products, respectively) both for the forward- and backward-scattered products. It suggests that the initially excited bending motion of the H–O–O moiety in the collisional HOOH complex primarily contributes to the product rotation. © 1999 American Institute of Physics.  
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82.30.Cf Atom and radical reactions; chain reactions; molecule-molecule reactions
82.30.Hk Chemical exchanges (substitution, atom transfer, abstraction, disproportionation, and group exchange)
34.50.Ez Rotational and vibrational energy transfer
33.20.Tp Vibrational analysis
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.50.Dq Fluorescence and phosphorescence spectra

Experimental and theoretical study of line mixing in methane spectra. I. The N2-broadened ν3 band at room temperature

D. Pieroni, Nguyen-Van-Thanh, C. Brodbeck, C. Claveau, A. Valentin, J. M. Hartmann, T. Gabard, J.-P. Champion, D. Bermejo, and J.-L. Domenech

J. Chem. Phys. 110, 7717 (1999); http://dx.doi.org/10.1063/1.478724 (16 pages) | Cited 15 times

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Line-mixing effects have been studied in the ν3 band of CH4 perturbed by N2 at room temperature. New measurements have been made and a model is proposed which is not, for the first time, strictly empirical. Three different experimental set ups have been used in order to measure absorption in the 2800–3200 cm−1 spectral region for total pressures in the 0.25–2 and 25–80 atm ranges. Analysis of the spectra demonstrates the significant influence of line mixing on the shape of the Q branch and of the P and R manifolds. A model is proposed which is based on state-to-state collisional transfer rates calculated from the intermolecular potential surface with a semiclassical approach. The line-coupling relaxation matrix is constructed from these data and two additional parameters which are fitted on measured absorption. Comparisons between measurements and spectra computed accounting for and neglecting line mixing are made. They prove the quality of the approach which satisfactory accounts for the effects of pressure and of rotational quantum numbers on the spectral shape under conditions where modifications introduced by line mixing are important. For high rotational quantum number lines, the main features induced by collisions are predicted but some discrepancies remain; the latter may be due to improper line-coupling elements but there is strong evidence that the use of inaccurate line broadening parameters also contributes to errors in calculated spectra. © 1999 American Institute of Physics.
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33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
33.20.Ea Infrared spectra
34.50.-s Scattering of atoms and molecules
33.70.Jg Line and band widths, shapes, and shifts
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)

Temperature, pressure, and perturber dependencies of line-mixing effects in CO2 infrared spectra. III. Second order rotational angular momentum relaxation and Coriolis effects in Π←Σ bands

J.-M. Hartmann, R. Rodrigues, Nguyen-Van-Thanh, C. Brodbeck, C. Boulet, R. Le Doucen, N. Lacome, and L. Bonamy

J. Chem. Phys. 110, 7733 (1999); http://dx.doi.org/10.1063/1.478723 (12 pages) | Cited 7 times

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The energy corrected sudden approach is used in order to deduce collisional parameters and to model infrared quantities in Π←Σ bands of CO2–He and CO2–Ar mixtures in the 200–300 K temperature range. Measured line-broadening coefficients and absorption in the Q-branch of the ν2 band at moderate pressure are first used for the determination (from a fit) of the time constant associated with the relaxation of the second order traceless tensor of the rotational angular momentum (all other collisional quantities have been determined previously). The results obtained are consistent with previous (calculated) temperature dependent values of the depolarized Rayleigh cross sections. The model is then successfully tested through computations of absorption in the ν2 and (ν1+ν2)I bands at elevated densities. Analysis of line-mixing effects is made, including study of the influence of interbranch transfers and of Coriolis coupling. Differences between the effects of collisions with He and Ar are pointed out and explained. © 1999 American Institute of Physics.
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33.20.Ea Infrared spectra
33.70.Jg Line and band widths, shapes, and shifts
33.20.Fb Raman and Rayleigh spectra (including optical scattering)
33.15.Mt Rotation, vibration, and vibration-rotation constants
33.20.Tp Vibrational analysis
34.50.-s Scattering of atoms and molecules

Ab initio potential energy surfaces for He–Cl2, Ne–Cl2, and Ar–Cl2

Sławomir M. Cybulski and Jennifer S. Holt

J. Chem. Phys. 110, 7745 (1999); http://dx.doi.org/10.1063/1.478683 (11 pages) | Cited 31 times

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The three-dimensional ground state potential energy surfaces for He–Cl2, Ne–Cl2, and Ar–Cl2 have been calculated using the single and double excitation coupled-cluster approach with noniterative perturbational treatment of triple excitations [CCSD(T)]. Calculations have been performed with the augmented correlation consistent triple zeta basis sets supplemented with an additional set of bond functions. Single point calculations for approximate minima have also been performed with several other basis sets including the quadruple zeta basis set (aug-cc-pVQZ) with bond functions. For He–Cl2 and Ar–Cl2 the CCSD(T) results show that the linear configuration is lower in energy than the T-shaped one. For Ne–Cl2 the CCSD(T) approach predicts the T-shaped configuration to be lower in energy. The linear configuration has been found to be more sensitive than the T-shaped one to the changes of the Cl–Cl bond length with the interaction becoming weaker when the Cl–Cl bond length is shortened from its equilibrium value and stronger when it is lengthened. More detailed analysis shows that sensitivity of component energies such as exchange, dispersion, and induction is much greater than that of supermolecule results. The interaction in the T-shaped configuration becomes slightly stronger for shorter Cl–Cl bonds. For He–Cl2 and Ar–Cl2 the larger zero-point vibrational energy of the linear configuration is responsible for making the T-shaped configuration the ground vibrational state. Vibrational effects further increase the difference in energy between the ground state T-shaped configuration of Ne–Cl2 and its linear counterpart. © 1999 American Institute of Physics.
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31.15.A- Ab initio calculations
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
31.15.bw Coupled-cluster theory
33.15.Bh General molecular conformation and symmetry; stereochemistry

Theoretical study on quantum control of photodissociation and photodesorption dynamics by femtosecond chirped laser pulses

Kenji Mishima and Koichi Yamashita

J. Chem. Phys. 110, 7756 (1999); http://dx.doi.org/10.1063/1.478684 (14 pages) | Cited 20 times

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We have theoretically studied the effect of chirping one-photon incident laser pulses on (I) the branching ratio of the HOD molecule in the photochemical reaction D+OH←HOD→H+OD and (II) the UV photodesorption dynamics of NH3 and ND3 from Cu(111). As was predicted in our previous 1D model, wave packet calculations have demonstrated that it is possible, in practice, to control the branching ratio of reaction (I) and to greatly enhance the desorption probability of the photodesorption reaction (II) by negatively chirped laser pulses. It was found that two characteristics of (negatively) chirped laser pulses contribute to this remarkable effect; the mechanism of adiabatic rapid passage for the population transfer between the ground and excited states, and the intrapulse pump-dump process for determining the branching ratio and photodesorption yield. © 1999 American Institute of Physics.
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33.80.Gj Diffuse spectra; predissociation, photodissociation
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
68.03.Fg Evaporation and condensation of liquids
68.43.Mn Adsorption kinetics
79.20.La Photon- and electron-stimulated desorption
42.60.Fc Modulation, tuning, and mode locking
42.65.Re Ultrafast processes; optical pulse generation and pulse compression

Structural transition in hot small clusters

D. I. Zhukhovitskii

J. Chem. Phys. 110, 7770 (1999); http://dx.doi.org/10.1063/1.478685 (9 pages) | Cited 12 times

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At relatively high temperatures (higher than the melting temperature of a liquid), clusters existing in the supersaturated vapor are characterized by an intense internal motion of molecules. The virtual chains model of small “hot” clusters is proposed, which assumes that the number of bonds in small clusters is minimal, and that their structure is chainlike. Interpolation formulas for extensive thermodynamic functions of a cluster containing arbitrary number of atoms are found. Validity of model assumptions are verified by the molecular dynamics simulation for the ensemble with constant temperature and pressure. Simulation results are discussed, among which are the average potential energy of a cluster, the radial distribution function, and topological structure of clusters. Numerical results validate the basic assumption of proposed model. © 1999 American Institute of Physics.
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36.40.Ei Phase transitions in clusters
64.70.F- Liquid-vapor transitions
65.20.-w Thermal properties of liquids
65.40.gd Entropy

Benchmark enthalpies of formation and binding energies of proton-bound pairs between HCN and HCN, NH3, H2O, and HF

Paul M. Mayer

J. Chem. Phys. 110, 7779 (1999); http://dx.doi.org/10.1063/1.478686 (10 pages) | Cited 6 times

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The relative thermochemical properties of cluster ions (solvation enthalpies, entropies, and free energies) can be obtained from experimental techniques such as high pressure mass spectrometry and selected-ion flow tube mass spectrometry. Theory can play an important role in these studies by providing both accurate binding energies of the smaller members of the cluster families and insight into the structure and bonding in the cluster ions. This study assesses the performance of a variety of levels of ab initio and density functional theories for predicting the structures and energies of one family of cluster ions, the proton-bound dimers between HCN and HCN, NH3, H2O, and HF. The theoretical procedures were assessed based on their performance relative to high-level treatments such as QCISD(T) correlation, the 6-311+G(2df,p) basis set, and G2 energy calculations. The results of the assessment indicate that MP2/6-31G(d) optimized geometries are sufficient for the calculation of binding energies and heats of formation with advanced methods such as G2. Further increases in basis set size and electron correlation improve the geometries of the dimers, but these geometric changes have little impact on the final high-level energy calculations. The heats of formation and binding energies of the clusters are best described by G2 theory, but modified versions of G2 such as G2(MP2) and G2(MP2,SVP) also provide reliable values. Calculated binding energies of these four proton-bound dimers are compared to available experimental values from the literature, and the effect of basis set superposition error is examined © 1999 American Institute of Physics.
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82.60.Cx Enthalpies of combustion, reaction, and formation
33.15.Ta Mass spectra
31.15.A- Ab initio calculations
31.15.E- Density-functional theory
31.15.vq Electron correlation calculations for polyatomic molecules

Global nine-dimensional potential energy surface for the H5 system. I. Ab initio multiple reference single and double excitation configuration interaction computations

Alfredo Aguado, César Tablero, and Miguel Paniagua

J. Chem. Phys. 110, 7789 (1999); http://dx.doi.org/10.1063/1.478687 (7 pages) | Cited 2 times

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The ground-state adiabatic potential energy surface was computed for 2836 conformations of H5, using a multiple reference single and double excitation configuration interaction program and an extended basis set. The transition state obtained is that of a pentagon with D5h symmetry. We find the energy barrier to lie at 81 kcal/mol within ±1 kcal/mol if a multireference Davidson’s correction is employed, while the De(H2) at this level was 109 kcal/mol. The calculations presented here clearly show the energy of H5 in D5h symmetry to be 28 kcal/mol below the dissociation energy of H2, and therefore a bimolecular mechanism, in the presence of hydrogen atoms, could indeed be considered for the exchange process: H2+D2+H→2HD+H. © 1999 American Institute of Physics.
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31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
82.20.Kh Potential energy surfaces for chemical reactions
31.15.A- Ab initio calculations
31.15.vq Electron correlation calculations for polyatomic molecules
33.15.Fm Bond strengths, dissociation energies

Global nine-dimensional potential energy surface for the H5 system. II. Fit to an analytical expression

César Tablero, Alfredo Aguado, and Miguel Paniagua

J. Chem. Phys. 110, 7796 (1999); http://dx.doi.org/10.1063/1.478688 (6 pages) | Cited 4 times

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A global nine-dimensional potential energy surface (GPES) for the adiabatic ground state of the H5 system which fits the ab initio data, reported in the previous paper of this series, has been obtained (root-mean-square error 2.2 kcal/mol). The global fitting procedure is an extension of the corresponding procedure for triatomic and tetra-atomic systems including the functional form previously proposed by the authors. The H5 GPES obtained here is totally symmetric with respect to permutations of the hydrogen atoms and satisfies the criteria needed to be used in scattering calculations. © 1999 American Institute of Physics.
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31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
31.15.A- Ab initio calculations

Ab initio investigation of the vibronic spectrum involving the two lowest-lying electronic states of HCCO

Boris Schäfer, Miljenko Perić, and Bernd Engels

J. Chem. Phys. 110, 7802 (1999); http://dx.doi.org/10.1063/1.478803 (9 pages) | Cited 13 times

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The results of ab initio calculations of the vibronic spectra involving both lowest-lying states X2A″ and A2A′ of the ketenyl radical HCCO are presented. Potential energy surfaces are computed by means of the coupled cluster method with perturbative triple corrections [CCSD(T)]. A recently developed ab initio approach for the treatment of the Renner–Teller effect in tetra-atomic asymmetric molecules is applied to calculate the vibronic energy levels. © 1999 American Institute of Physics.
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31.15.A- Ab initio calculations
33.20.Wr Vibronic, rovibronic, and rotation-electron-spin interactions
31.90.+s Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)
31.15.bw Coupled-cluster theory

State-to-state rate coefficients for H+H2

M. E. Mandy and P. G. Martin

J. Chem. Phys. 110, 7811 (1999); http://dx.doi.org/10.1063/1.478731 (10 pages) | Cited 5 times

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We have used the quasiclassical trajectory (QCT) method to determine state-to-state rate coefficients for all transitions among the 348 (v,j) states of the ground electronic state (Σg+) of the hydrogen molecule caused by collision with a hydrogen atom. Direct and indirect results were combined to give best possible rate coefficients within the quasiclassical approximation. Because energy transfer behavior differs for reactive and nonreactive channels and these channels are distinguishable classically, it is appropriate to consider separately the rate coefficients for each channel. Where available, quantum cross sections were incorporated into our calculation. The temperature dependence of the rate coefficients is parametrized over the temperature range 600 to 10 000 K. We use this complete set of state-to-state rate coefficients to test several scaling laws. © 1999 American Institute of Physics.
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34.50.-s Scattering of atoms and molecules

Experimental and theoretical determination of the magnetic dipole transition moment for the Br(4p5)(2P1/2←2P3/2) fine-structure transition and the quantum yield of Br(2P1/2) from the 193 nm photolysis of BrCN

G. He, Michael Seth, I. Tokue, and R. Glen Macdonald

J. Chem. Phys. 110, 7821 (1999); http://dx.doi.org/10.1063/1.478689 (11 pages)

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The integrated-absorption coefficients of several hyperfine lines of the magnetic dipole allowed transition of the bromine atom, Br, center at 3685.2 cm−1 were measured, and a value for the square of the magnetic dipole transition moment of the Br atom was determined. A theoretical calculation for the magnetic dipole transition moment was also carried out using a relativistic ab initio atomic structure formulation. The theoretical value was in excellent agreement with the value predicted assuming pure LS coupling, and in reasonable agreement with experiment. The Br atom was generated in equal concentration with the cyano radical (CN) by the 193 nm photolysis of cyanogen bromine, BrCN. The CN radicals were titrated by the rapid reaction with C3H8 to generate HCN and a small amount of HNC. Both time-resolved and frequency-scanned infrared absorption spectroscopy were used to monitor the Br, HCN, and HNC species. The photolysis of BrCN at 193 nm produced both the ground state Br(2P3/2) and the spin-orbit excited Br(2P1/2) atoms, and the yield for the production of Br(2P1/2) atoms was measured to be 0.31±0.01. The rate constants for the quenching of Br(2P1/2) by BrCN and C3H8 at 293 K were also determined. © 1999 American Institute of Physics.
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32.70.Cs Oscillator strengths, lifetimes, transition moments
32.30.Rj X-ray spectra
82.50.Bc Processes caused by infrared radiation
82.50.Hp Processes caused by visible and UV light
32.30.Bv Radio-frequency, microwave, and infrared spectra
33.20.Ea Infrared spectra

Intermolecular forces from density functional theory. III. A multiproperty analysis for the Ar(1S)-CO(1Σ) interaction

F. A. Gianturco, F. Paesani, M. F. Laranjeira, V. Vassilenko, and M. A. Cunha

J. Chem. Phys. 110, 7832 (1999); http://dx.doi.org/10.1063/1.478690 (14 pages) | Cited 19 times

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The full anisotropic interaction between one Ar atom and the CO(1Σ) molecule treated as a rigid rotor (RR) at its equilibrium geometry is evaluated using density functional theory (DFT) to describe the short-range repulsive region (and its orientational anisotropy) as well as the well region and its angular dependence. The long-range dispersion forces are added from the results of perturbation theory and a scaling procedure is suggested for their correct matching with the DFT data. The computational results are found to agree very well with more sophisticated calculations and to improve on earlier empirical estimates. An extensive comparison with available transport property measurements is also carried out and using, among others, new experimental data for thermal diffusion [Shashkov et al., Inzh. Fiz. Zh. 71, 182 (1998)] analyzed in this work for the first time. The present modifications of DFT treatment of the interaction using the correct dispersion terms therefore appears to provide a realistic description of the Ar–CO potential and of several dynamical properties of this molecular mixture in the gas phase. © 1999 American Institute of Physics.
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34.20.Gj Intermolecular and atom-molecule potentials and forces
31.15.E- Density-functional theory
31.15.xp Perturbation theory

Electronic isomers in [(CO2)nROH]− cluster anions. I. Photoelectron spectroscopy

Tatsuya Tsukuda, Morihisa Saeki, Ryoichi Kimura, and Takashi Nagata

J. Chem. Phys. 110, 7846 (1999); http://dx.doi.org/10.1063/1.478691 (12 pages) | Cited 19 times

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Photoelectron spectra of [(CO2)n−1ROH]− (R=H and CH3) with 2 ⩽ n ⩽ 7 have been measured at a photon energy of 4.66 eV. Analysis of the photoelectron band envelopes has revealed that the spectra of [(CO2)n−1H2O]− with 3 ⩽ n ⩽ 5 consist of two band components. The maximum of each component corresponds to the vertical detachment energy (VDE) of the relevant anionic species. In each spectrum the VDE values for the two components differ by ≈1 eV. For example, the [(CO2)4H2O]− spectrum is characterized by two VDE values of 2.63±0.04 and 3.71±0.06 eV. From the VDE difference, we conclude that the observed two components arise from isomers having different electronic structures, and that these “electronic isomers” can be designated as C2O4−⋅H2O(CO2)n−3 and CO2−⋅H2O(CO2)n−2. Coexistence of electronic isomers occurs also in [(CO2)n−1CH3OH]−, but only at n = 3. The [(CO2)n−1CH3OH]− anions with n ≠ 3 display photoelectron spectra composed of a single broad band, which corresponds to photodetachment from CO2−⋅CH3OH(CO2)n−2 structure. The CO2−⋅ROH(CO2) isomers (n = 3) are found to be distinguishable from C2O4−⋅ROH by selective photodepletion at 532 nm during the time of flight in the mass spectrometer, implying that the two electronic isomers of [(CO2)2ROH]− coexist without interconversion. In contrast, it is revealed that [(CO2)4H2O]− (n = 5) are fluctuating between C2O4−⋅H2O(CO2)2 and CO2−⋅H2O(CO2)3 structures. Based on these experimental findings, combined with results obtained by recent ab initio calculations, a possible isomerization mechanism operative in [(CO2)n−1ROH]− is proposed. © 1999 American Institute of Physics.
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33.60.+q Photoelectron spectra
33.15.Bh General molecular conformation and symmetry; stereochemistry
36.40.Mr Spectroscopy and geometrical structure of clusters
36.40.Cg Electronic and magnetic properties of clusters
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