On the systematics of vibrational relaxation in polyatomic molecules

The systematic variation of vibrational relaxation rates with initial excitation, i.e., the quantum number scaling, is investigated for collisions involving polyatomic molecules. We consider the contrasting behavior of diatomic and polyatomic relaxation and the impact of the more varied behavior in polyatomics on experimental measurements. Particular emphasis is placed on the effect of collision-induced intramolecular vibrational transitions on the rate scaling. The theory utilized to accomplish such an analysis involves an extension of the energy corrected (ECS) scaling relationship to polyatomic vibrational transitions. This development is presented for vibrationally inelastic processes in a single electronic level. We apply the theory to the inversion of total rates for bending mode relaxation in CF2. The resulting state-to-state rates display peculiarities which reflect both the energy spectrum of the CF2 molecule and the nature of the collision partner.