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

Geleijns, Michel; van der Avoird, Ad; Wormer, Paul E. S.; Halberstadt, Nadine
October 2002
Journal of Chemical Physics;10/22/2002, Vol. 117 Issue 16, p7562
Academic Journal
We calculated the cross sections for vibrational predissociation of methane-Ar induced by excitation of the methane v[sub 3] mode. We used the ab initio CH[sub 4]-Ar potential depending explicitly on the ν[sub 3] and ν[sub 1] normal coordinates of the CH[sub 4] monomer that is presented in the preceding paper. It was found that dissociation into CH[sub 4] fragments excited in the ν[sub 1] mode—a V → V' process with very low kinetic energy release—strongly dominates over direct dissociation into Ar and ground state CH[sub 4], 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 ν[sub 3] mode is related to the opening up of appropriate ν[sub 1] dissociation channels and the occurrence of rotational resonances in the ν[sub 1] continuum in the energy range of the quasibound ν[sub 3] levels. The rotational state distributions of the emerging ν[sub 1] excited methane fragment are predicted.


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