A new potential energy surface for vibration–vibration coupling in HF–HF collisions. Formulation and quantal scattering calculations

Abstract

We present new ab initio calculations of the HF–HF interaction potential for the case where both molecules are simultaneously displaced from their equilibrium internuclear distance. These and previous ab initio calculations are then fit to a new analytic representation which is designed to be efficient to evaluate and to provide an especially faithful account of the forces along the vibrational coordinates. We use the new potential for two sets of quantal scattering calculations for collisions in three dimensions with total angular momentum zero. First we test that the angular harmonic representation of the anisotropy is adequate by comparing quantal rigid rotator calculations to those carried out for potentials involving higher angular harmonics and for which the expansion in angular harmonics is systematically increased to convergence. Then we carry out large-scale quantal calculations of vibration–vibration energy transfer including the coupling of both sets of vibrational and rotational coordinates. These calculations indicate that significant rotational energy transfer accompanies the vibration-to-vibration energy transfer process.

Analytical Potentials for HF Dimer and Larger HF Clusters from ab Initio Calculations

“…As a result of the spectroscopic studies [1][2][3][4][5][6][7][8][9][10][11][12] very accurate structural parameters, dissociation energies, and several fundamental vibrational frequencies are available. There have been extensive theoretical studies of the HF dimer, [13][14][15][16][17][18][19][20][21][22][23][24][25][26] many of which focus on the determination of structure and energy at the equilibrium geometry. More extensive calculations were presented by Bunker et al in a series of papers.…”

“…As a result of the spectroscopic studies − very accurate structural parameters, dissociation energies, and several fundamental vibrational frequencies are available. There have been extensive theoretical studies of the HF dimer, − many of which focus on the determination of structure and energy at the equilibrium geometry. More extensive calculations were presented by Bunker et al in a series of papers. − They computed the energy of the dimer at a very large number of different geometries using the averaged coupled pair functional theory (ACPF), and fitted the results to an analytic function, which they used to calculate the lowest intermolecular vibration levels.…”

Supercomputer Chemistry At the University of Minnesota

“…The largest calculations we have performed so far were carried out on the CYBER 205 and involved three energies, 450 sectors, 1,358 channels, and about 4 x 10'3 floating point operations (Schwenke and Truhlar, 1988). A slightly smaller calculation was actually sufficient to converge the vibration-to-vibration energy transfer for the first time for a qualitatively realistic intermolecular potential function .…”