Energy Transfer in the 2 u (1 D 2) Ion-Pair State of I2 by Inelastic Collisions with Noble Gas Atoms.

Abstract

We investigated the energy transfer in the 2u (1D2) ion-pair state of I2 by collision with noble gas atoms, Ar, Kr, and Xe, using an optical–optical double resonance/fluorescence detection technique. By analyzing the temporal profiles of the emission from the laser-excited 2u (1D2) state at various noble gas pressures, the quenching rate constants were determined to be (4.55 ± 0.42) × 10–10, (4.23 ± 0.11) × 10–10, and (6.83 ± 0.16) × 10–10 cm3 molecule–1 s–1 for quenching by Ar, Kr, and Xe, respectively. The 2g (1D2) ion-pair state, lying in the vicinity of the 2u (1D2) state, was identified as a destination state by collision with Ar and Kr. Collision with Xe provided a new reactive pathway forming the excimer XeI(B). The rate constants were determined to be = (9.61 ± 0.63) × 10–11 cm3 molecule–1 s–1 and = (4.87 ± 0.34) × 10–11 cm3 molecule–1 s–1 for the formation of the 2g (1D2) state by collision with Ar and Kr, respectively, and = (6.55 ± 0.19) × 10–11 cm3 molecule–1 s–1 for the formation of XeI(B). The collisional cross sections calculated from the quenching rate constants were considerably larger than the molecular size, owing to the harpoon mechanism.