Energy Transfer in the 2_u (¹D₂) Ion-Pair State of I₂ by Inelastic Collisions with Noble Gas Atoms

We investigated the energy transfer in the 2_u (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 2_u (¹D₂) state at various noble gas pressures, the quenching rate constants Formula Presented 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 2_g (¹D₂) ion-pair state, lying in the vicinity of the 2_u (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 Formula Presented = (9.61 ± 0.63) × 10^–11 cm³ molecule^–1 s^–1 and Formula Presented = (4.87 ± 0.34) × 10^–11 cm³ molecule^–1 s^–1 for the formation of the 2_g (¹D₂) state by collision with Ar and Kr, respectively, and Formula Presented = (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.