Collision-Induced Electronic Energy Transfer From v=0 Of The E(0+g) Ion-Pair State In I2: Collisions With He And Ar

The electronic energy transfer pathways that occur following collisions between I 2 in the E ion-pair electronic state ͑vϭ0, Jϭ55͒ and He and Ar atoms have been determined. The nearby D, DЈ, and ␤ ion-pair states are populated, but with relative branching ratios that vary with the rare gas collision partner. In He/I 2 collisions, the D state is preferentially populated, while Ar/I 2 collisions preferentially populate the ␤ electronic state. Bimolecular rate constants and effective hard sphere collision cross sections have been determined for each channel; the cross sections range from 7.0Ϯ1.0 Å 2 for populating the ␤ state with Ar collisions to 0.9Ϯ0.2 Å 2 for populating the DЈ state with He collisions. For both rare gas collision partners, and all three final electronic states, low vibrational levels are populated, in rough accord with the relevant Franck–Condon factors. There is little propensity observed for population of vibrational levels that are in near resonance with the initially prepared level in the E state.