THE H- CO STATE DISTRIBUTIONS AND TRANSLATIONAL ENERGY FROM TIME-RESOLVED INFRARED-ABSORPTION SPECTROSCOPY(OCS HOT ATOM REACTION )

Time-resolved infrared diode laser spectroscopy has been used to probe CO internal and translational excitation from the reaction of hot H a toms with OCS. Product distributions should be strongly biased toward the maximum 1.4 eV collision energy obtained from 278 nm pulsed photol ysis of HI. Rotations and vibrations are both colder than predicted by statistical density of states theory, as evidenced by large positive surprisal parameters. The bias against rotation is stronger than that against vibration, with measurable population as high as v = 4. The av erage CO internal excitation is 1920 cm-1, accounting for only 13 % of the available energy. Of the energy balance, time-resolved sub-Dopple r line shape measurements show that more than 38% appears as relative translation of the separating CO and SH fragments. Studies of the rela xation kinetics indicate that some rotational energy transfer occurs o n the time scale of our measurements, but the distributions do not rel ax sufficiently to alter our conclusions. Vibrational distributions ar e nascent, though vibrational relaxation of excited CO is unusually fa st in the OCS bath, with rates approaching 3% of gas kinetic for nu = 1. At 9720 cm-1 above the activation barrier, energy partitioning is c onsistent with incomplete IVR in an HSCO intermediate, followed by rep ulsive release of a large fraction of the available energy into relati ve translation.