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Collision cross sections for rotational and vibrational excitation of CO by fast H atoms are calculated for two potential energy surfaces, the older Bowman–Bitman–Harding potential and the recently constructed surface of Werner, Keller, and Schinke. Both quantum mechanical and classical calculations are performed. The results obtained with the new potential energy surface are very similar to those obtained with the older potential; in particular, they do not rectify the discrepancies between the experimental and theoretical cross sections for vibrationally elastic transitions into small rotational states of CO. © 1996 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The generalized Hess method (GHM) gives a line shape expression which is formally equivalent to the Rautian–Sobel’man hard collision model of Dicke narrowing, but differs radically in the definition of one of the relaxation terms. The relaxation term leading to pressure broadening is the same, but the term leading to Dicke narrowing and ultimately to Doppler line shapes at zero density differs in certain important respects: (1) in GHM it is a weighted sum of the pressure broadening coefficient and an optical diffusion coefficient and (2) there is no sharp distinction between ‘‘velocity changing’’ and ‘‘phase changing’’ collisions. The Dicke narrowing term should thus be understood as including both collision types irretrievably intermixed, with GHM providing a prescription for both relaxation terms. Applied to HF v=0→1, j→j±1 absorption spectra in a bath of Ar and using an accurate interaction potential obtained from spectra of the van der Waals complex and essentially exact close coupling scattering S matrices, GHM provides a rather good description of recently measured line shapes. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

Time dependent diode laser spectroscopy was used to measure Doppler profiles of P-branch lines in the fundamental vibrational band of CO shortly after collisions with H atoms having a translational energy of 2.3 eV. Observed spectral line profiles reflect two Doppler components, a negative room temperature component from molecules scattered out of a given v=0, J state, and a hot component from molecules scattered into the same state. Observed profiles are explained qualitatively using state-to-state differential cross sections calculated from the ab initio potential energy surface of Bowman, Bittman, and Harding and a rigid rotor coupled states quantum scattering approximation. © 1994 American Institute of Physics. [ABSTRACT FROM AUTHOR]

We have calculated the interaction for H2O–H2 at 722 points on a five-dimensional surface where both molecules are treated as rigid rotators and we have fitted the ab initio points to a 48-term angular expansion of products of spherical harmonics and rotation matrices. The resulting potential energy function shows strong angle dependence with a large contribution from electrostatic interactions. When averaged over H2 orientations, the resulting water-atom-like surface is found to have zero crossing and minimum at similar distances to the corresponding H2O–He surface but to be generally more repulsive at short range and more attractive at long range. The isotropic average of the potential has a zero-crossing radius σ=3.05 Å and a well depth ε=49.5 cm-1 at an intermolecular separation Rm=3.52 Å. [ABSTRACT FROM AUTHOR]

An interaction potential for H2O–Ar that was recently determined from spectra of the van der Waals complex [R. C. Cohen and R. J. Saykally, J. Chem. Phys. 94, 7991 (1990)] is used with accurate molecular scattering calculations to predict line broadening parameters for the 183 and 380 GHz transitions of water vapor. Theoretical values are about 15% higher than experiment. [ABSTRACT FROM AUTHOR]