Recent Theoretical Results of Rotational-Translational Energy Transfer

Abstract

Theoretical work is reviewed on scattering calculations and tests of some ab initio interaction potentials representing simple systems by subsequent calculations of differential, integral, and effective cross sections. The interaction potentials of He-H₂ published by Meyer, Hariharan, and Kutzelnigg have been composed in one vibrotor potential grid which has been used to calculate effective cross sections describing relaxation phenomena. Good agreement with recently measured data has been achieved. Deviations from results previously derived from the well-known Shafer-Gordon potential fit are discussed. The present quality of the H₂-H₂ interaction potential is shown: Some comparisons with experiments give evidence for sufficient accuracy of the rotationally inelastic cross sections of H₂-H₂ and isotopic systems, in the low temperature regime. The remaining disagreement with measurements of the undulatory structure of the total differential cross sections and of low temperature second virial coefficients has been removed by determining a distance dependent scaling function applicable to the full vibrotor potential, under the condition that the measured second virial coefficients can be obtained quantitatively, and the relative anisotropies of the system are conserved. Dimer bound states and pair correlation functions have been calculated in this fit procedure. A first step of improvement is reported for an ab initio potential of He-CO published by Thomas, Kraemer, and Diercksen. Measurements of sometime of flight profiles and one total differential cross section have been reproduced theoretically after applying scaling procedures to the potential.