Experimental and theoretical study of the vibrational relaxation of CO(ν = 1) and N 2(ν = 1): V-T relaxation by the isotopes of helium

Abstract

Experimental results are reported for the rate constants for the vibrational relaxation of CO(ν = 1), 14N 2(ν = 1) and 15N 2(ν = 1) by 3He and 4He in the temperature range from 300-80 K. These are compared to rate constants determined from the numerical solution of the quantum scattering equations. It is shown that the infinite-order sudden approximation can be used to reduce the number of coupled channels to those required for the vibrational levels. The calculations are applied to ab initio potentials and a model based on the anisotropic Morse potential. The major features which govern the rate of vibrational deactivation are shown to be the energy of the vibrational quantum, the mass of the collision partner and the steepness of the repulsive part of the intermolecular potential. Including an attractive well in the potential preferentially increases the relaxation rate constants at low temperatures. The roles of the attractive terms and the anisotropy of the potential in the deviations of the experimental data from the Landau-Teller predictions are discussed.