Reactions of electronically excited iodine atoms I(52P½) with Cl2, Br2, ICl and IBr

Abstract

Electronically excited iodine atoms, I(5²P_½), have been generated by the flash photolysis of CF₃I. The excited atoms have been monitored by time-resolved absorption spectroscopy both in the ultra-violet and the vacuum ultra-violet, together with the products of their reactions with Cl₂, Br₂, ICl and IBr. The decay of I(5²P_½) in the presence of these gases is dominated by exothermic, metathetical reactions such as I(5²P_½)+ Cl₂→ICl + Cl, where Cl₂ and ICl are in their electronic ground states. The analogous reactions of I(5²P_3/2), are endothermic and do not contribute significantly under the experimental conditions. Collisionally induced spin orbit relaxation of I (5²P_½) into ground state atoms. I(5²P_3/2) with Cl_{2, Br2}, ICl and IBr are 2.1 × 10^–13, 1.5 × 10^–12, 3.4 × 10 ^–12, and 4.3 × 10^–12 cm³ molecule ^–1 sec^–1, respectively. A comparison may be made with the rate constants for the analogous reactions of I(5²P_3/2) from data for the reverse reactions combined with equilibrium constants, calculated by statistical mechanics.