QUANTUM SYMMETRY RESTRICTIONS IN STATE-TO-STATE INELASTIC SCATTERING FROM $S_{1}$ GLYOXAL

Abstract

A laser pump-dispersed fluorescence probe approach has been used to monitor state-to-state inelastic scattering in $S_{1} (^{1}A_{u})$ trans-glyoxal (CHO-CHO) by a variety of collisionpartners. These experiments have been benchmarks for the fully quantal three-dimensional theoretical calculations of Clary, Kroes and coworkers. Their azimuthal and vibrationally close-coupled, infinite-order-sudden (AVCC-IOS) calculations predict that excitation of the low frequency torsional mode must also involve a change in angular momentum. This selection rule is derived directly from symmetry arguments in the close-coupled matrix elements. Experiments were designed to investigate these predictions further, and involve glyoxal $0^{0}K^{n} + H_{2}$ or He where $n = 0, 2$ and 3. The results show that quantum symmetry effects are present but not to the extent of the theoretical predictions. G.-J. Kroes and R.P.H. Rettschnick, J. Chem. Phys. 94, 360-374 (1994). G.-J. Kroes, R.P.H. Rettschnick, and D.C. Clary, Chem. Phys. 148, 359-379 (1990).