Photodissociation of the methane-argon complex. II. Vibrational predissociation dynamics, spectral linewidths and fragment state distributions

摘要

We calculated the cross sections for vibrational predissociation of methane-Ar induced by excitation of the methane nu(3) mode. We used the ab initio CH4-Ar potential depending explicitly on the nu(3) and nu(1) normal coordinates of the CH4 monomer that is presented in the preceding paper. It was found that dissociation into CH4 fragments excited in the nu(1) mode-a V-->V' process with very low kinetic energy release-strongly dominates over direct dissociation into Ar and ground state CH4, and is responsible for the line broadening observed experimentally. The strong variation of the linewidths, observed as well as calculated, for the van der Waals levels excited in combination with the nu(3) mode is related to the opening up of appropriate nu(1) dissociation channels and the occurrence of rotational resonances in the nu(1) continuum in the energy range of the quasibound nu(3) levels. The rotational state distributions of the emerging nu(1) excited methane fragment are predicted. (C) 2002 American Institute of Physics. [References: 53]