Collisional deactivation of Br(4 2P1/2) by hydrogen isotopes

The quenching of electronically excited bromine atoms Br(4 2P1/2) upon collision with H2, HD, and D2 has been studied at 300 degreeK. The temporal profile of the Br(4 2P1/2) concentration was monitored by observation of the time-resolved attenuation of bromine resonance radiation at 153.2 nm. The probabilities of deactivation by the hydrogen isotopes are presented and compared to theoretical treatments based either upon long-range coupling via mulitpolar interactions or explicit treatment of the nonadiabatic crossing probabilities computed using semiempirical potential surfaces. These results are then examined with a view toward assessing the importance of near-resonant electronic--vibrational energy transfer in such an elementary system