Very low energy collision induced vibrational relaxation of 1A/sub u/ glyoxal

We report the results of a study of very low energy collision induced vibrational relaxation of 1A/sub u/ glyoxal. The effective collision energy is found to be different for different initial vibronic states, and the final states populated are drawn from a small subset of all available final states. The observed pathways of relaxation are interpreted using a previously proposed orbiting resonance model for the He: glyoxal collisions. It is inferred that (i) single collision--single quantum transfers dominate the relaxation process, and (ii) when there are near degeneracies in the vibrational manifold the lowering of symmetry in the orbiting resonance can permit mode mixing that is prohibited in the isolated molecule