Joel M. Bowman

Self‐consistent field energies and wavefunctions for coupled oscillators

We formulate a self‐consistent field description of coupled anharmonic oscillators. The SCF equations are solved numerically for a model problem of two coupled anharmonic oscillators and energy eigenvalues compared with previously published exact quantum and semiclassical ones.

Investigations of self-consistent field, scf ci and virtual stateconfiguration interaction vibrational energies for a model three-mode system

Abstract Self-consistent field vibrational energy eigenvalues are reported for a model three-mode system considered previously by Noid et al. These eigenvalues and those from configuration interaction calculations based on true SCF wavefunctions and virtual state wavefunctions are compared with the previous semiclassical and exact quantum ones of Noid et al.

Ab initio calculations of electronic and vibrational energies of HCO and HOC

The ab initio calculation of electronic energies for numerous configurations of HCO and HOC, and a novel method for fitting the energies to a global surface are reported. This surface is used to calculate all the bound vibrational states of nonrotating HCO and DCO using the Watson Hamiltonian. Some quasibound vibrational states are also reported for nonrotating HOC for energies below the HOC saddle point energy. Comparisons of the HCO and DCO vibrational energies are made with recent experimental results.

Vibrational energy levels of formaldehyde

Vibrational energies for nonrotating H2CO and D2CO are calculated using unadjusted and adjusted ab initio quartic force fields in normal mass‐weighted coordinates. Converged energies are obtained using uncoupled anharmonic oscillator and vibrational self‐consistent field basis sets and are compared with experiment. Strong ‘‘Fermi‐like’’ resonances are found involving the CH symmetric and antisymmetric stretches.

Sudden rotation reactive scattering: Theory and application to 3‐D H+H2

An approximate quantum mechanical theory of reactive scattering is presented and applied to the H+H2 reaction in three dimensions. Centrifugal sudden and rotational sudden approximations are made in each arrangement channel, however, vibrational states are treated in a fully coupled manner. Matching of arrangement channel wave functions is done where the arrangement channel centrifugal potentials are equal. This matching is particularly appropriate for collinearly favored reactions. Integral and differential cross sections are calculated for the H+H2 reaction for H2 in the ground and first excited vibrational states. These calculations employ the Porter–Karplus potential energy surface mainly to allow for comparisons with previous accurate and approximate quantal and quasiclassical calculations.

Sudden rotation calculations of atom–molecule scattering

Rotational inelastic cross sections for two atom–rigid rotor systems, 4He+H2(j) and 4He+I2* (j), have been calculated using a quantal sudden approximation that we term the sudden rotation approximation. Vibrational inelastic cross sections have also been calculated for 4He+H2(ν,j) using a two and three vibration basis set for total energies between 1.2 and 4.2 eV. The present results for 4He+H2 are compared with the coupled channel and coupled states results of McGuire and Kouri and with the two vibration results of McGuire. The 4He+I2* results are compared with quasiclassical trajectory calculations and the experiments of Steinfeld and co‐workers.

Complex coordinate calculations of Feshbach resonance energies and widths for a collinear triatomic system

Complex resonance energies are calculated for a model triatomic system studied previously by Eastes and Marcus [W. Eastes and R. A. Marcus, J. Chem. Phys. 59, 4757 (1973)]. The complex coordinate method is employed to obtain resonance positions and widths for six states. The positions are all in excellent agreement with previous scattering and stabilization results and there is also good agreement with the one width obtained previously from scattering calculations. The additional widths obtained are given for the first time. Some speculations about possible laser induced absorption and emission among these resonances and true bound states are made.

A comparative study of the reaction dynamics of several potential energy surfaces of O(3P)+H2→OH+H. I

Two new potential energy surfaces for th O+H2→OH+H reaction are presented, and a detailed comparision of the saddle point properties and thermal rate constants of these and of six other O+H2 surfaces is made. The two new surfaces are (1) an extended BEBO surface and (2) a rotated‐Morse‐oscillator‐spine (RMOS) fit to the accurate ab initio POLCI surface of Walch and Dunning. In the BEBO surface, an improved end atom repulsive potential is used which leads to a much more accurate barrier estimate (11.52 kcal/mol) than with the usual anti‐Morse expression. The POLCI–RMOS surface is an essentially quantitative fit to the ab initio points, and has a barrier of 12.58 kcal/mole. The other O+H2 surfaces examined include the LEPS surface of Westenberg and de Haas (LEPS‐WDH) and of Johnson and Winter (LEPS‐JW), the diatomics‐in‐molecules (DIM) surface of Whitlock, Muckerman, and Fisher, the ab initio surface of Howard, McLean, and Lester (HML), and a fit to HML’s surface by Schinke and Lester (SL). For the LEPS‐JW ...

Rotational rainbows in inelastic atom—molecule differential cross sections☆

Abstract The existence of rotational raibows in atom-rigid rotor inelastic differential cross sections is shown by considering the classical limit of the centrifugal sudden-rotational sudden expression for the scattering amplitude.

An SCF-state interaction method for coupled oscillator systems☆

Abstract A computational method is presented for the treatment of coupled systems of oscillators by a SCF-like formalism. Extensions to state interaction (analogous to configuration interaction) are presented and explored numerically for the Henon—Heiles system. The formalism is presented for an MCSCF-like approach to such problems.