15min:

SAMUEL M. CLEGG, MARIANA D. DUCA AND CHARLES S. PARMENTER, Department of Chemistry, Indiana University, Bloomington, IN 47405.

A laser pump-dispersed fluorescence probe approach has been used to monitor state-to-state inelastic scattering from S₁ (¹A_u) trans -glyoxal in crossed molecular beams. The trio of collision partners H₂, He, and D₂ provided the unique opportunity to explore the relative influences of the center-of-mass collision energy (E_cm) versus the interaction potential energy surface (PES). The PES for glyoxal + H₂ (E_cm = 650cm^-1) and D₂ (770cm^-1) are identical but the relative cross sections are vastly different. In contrast, when the kinematics were matched, as in the case for glyoxal + He (770cm^-1) and D₂ (770cm^-1), the distribution of cross sections were nearly identical. These observations indicate that the collision kinematics dominate inelastic scattering while the details of the PES play a minor role. The experiments presented here were designed to investigate this kinematic control by selectively controlling the relative velocity and thus the center-of-mass collision energy and momentum.