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We investigated the energy transfer in the 2 u ( 1 D 2 ) ion-pair state of I 2 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 ( 1 D 2 ) state at various noble gas pressures, the quenching rate constants k q,2 Rg u were determined to be (4.55 ± 0.42) × 10 −10 , (4.23 ± 0.11) × 10 −10 , and (6.83 ± 0.16) × 10 −10 cm 3 molecule −1 s −1 for quenching by Ar, Kr, and Xe, respectively. The 2 g ( 1 D 2 ) ion-pair state, lying in the vicinity of the 2 u ( 1 D 2 ) 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 − k q,2 2 Ar u g = (9.61 ± 0.63) × 10 −11 cm 3 molecule −1 s −1 and − k q,2 2 Kr u g = (4.87 ± 0.34) × 10 −11 cm 3 molecule −1 s −1 for the formation of the 2 g ( 1 D 2 ) state by collision with Ar and Kr, respectively, and − k q,2 XeI Xe u = (6.55 ± 0.19) × 10 −11 cm 3 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.

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