Simple estimation of thermal capture rates for ion-dipole collisions by canonical effective potential methods

Abstract

Thermal capture rate coefficients are considered for collision partners which at long range interact by ion-dipole plus polarization potentials. The simple Langevin-Gioumousis-Stevenson theory is extended by mapping the true asymmetric multidimensional interaction potential onto an effective spherically symmetric potential obtained by analysis of canonical probability or flux equalities. Bound states are eliminated in the mapping as well as in the final rate coefficient. Capture rate coefficients are calculated for H 3 + ions colliding with HCl, CS and HCN in a model where the ion is represented as a point charge and the target as a diatomic molecule. Corresponding calculations are carried out using canonical variational transition state theory. The theoretical results are compared with corresponding results obtained in classical trajectory calculations wherein the diatomic target (HCl, CS or HCN) is modeled as two point charges.