Electronically nonadiabatic mechanism of the vibrational relaxation of NO in Ar: Rate coefficients from ab initio potentials and asymptotic coupling

Abstract

In this paper, the electronically nonadiabatic Landau-Zener (LZ) mechanism for the vibrational relaxation v = 1 → v = 0 of NO(XΠ) in collisions with Ar(S01) is discussed. It corresponds to nonadiabatic transitions between two crossing vibronic potential energy surfaces (PESs) originating from vibrational states of the collision complex and supported by two coupled electronic PESs. The LZ rate coefficients k10LZ are calculated within the uniform Airy approach in the reaction coordinate approximation with parameters derived from ab initio PESs and an asymptotic estimation of the Franck-Condon factor in the nonadiabatic coupling region. The rate coefficients are close to the experimental rate coefficients available over the range of 900-2500 K, where the electronically adiabatic Landau-Teller (LT) mechanism with the rate coefficients k10LT does not make a noticeable contribution to the total relaxation rate. The ratio k10LZ/k10LT increases with temperature and the LZ and LT mechanisms have comparable rates at about 4000 K.

The Dynamics of Highly Vibrationally Excited CO Scattered from Metal Surfaces

“…However, there are cases for which transitions between adiabatic potential energy surfaces-so-called electronically non-adiabatic transitions-need to be taken into account. For example, this has been recently discussed for the vibrational relaxation of NO(v = 1) in collisions with argon atoms [20]. In contrast to molecule-atom or moleculemolecule interactions, electronically non-adiabatic effects may play a more pronounced role in molecule-surface interactions, especially in the interaction of molecules with metal surfaces.…”