Further insight into the tunneling contribution to the vibrational relaxation of NO in Ar

Abstract

Tunneling corrections to Landau-Zener rate coefficients for the vibrational relaxation NO(X-2 Pi, nu = 1) + Ar -> NO(X-2 Pi, nu = 0) + Ar between 300 and 2000 K are determined employing ab initio potential energy surfaces calculated by the code provided by Alexander [J. Chem. Phys. 111, 7426 ( 1999)]. The calculations use a reaction coordinate approach and lead to vibronically nonadiabatic transition probabilities within the generalized Airy approximation as extended to the WKB under-barrier Landau-Lifshitz limit. The calculations confirm experimental evidence for an onset of major tunneling contributions to the relaxation rate at temperatures below about 900 K and rationalize large tunneling contributions at 300 K. These effects increase the rate coefficients by several orders of magnitude over the uncorrected Landau-Zener values and remove the large gap between the latter and experimental results. (C) 2015 AIP Publishing LLC.