Study of electronically excited iodine atoms, I(5²P_½), in the presence of alkyl iodides

Abstract

ion of an iodine atom from an alkyl iodide by an electronically excited iodine atom, I(52P½), is an exothermic process and thus may compete with collisional quenching at room temperature. I(52P½), generated by the flash photolysis of CF3I, has been monitored by kinetic spectroscopy in absorption in the ultra-violet in the presence of seven alkyl iodides. The overall second-order rate constants for the removal of I(52P½) at ∼300°K were 1.7 × 10–12, 1.9 × 10–13, 2.0 × 10–13, 2.0 × 10–13, 2.9 × 10–13, 2.9 × 10–13 and 3.8 × 10–13 cm3 molecule–1 sec–1 for CH3I, C2H5I, n-C3H7I, i-C3H7I, n-C4H9I, i-C4H9I and t-C4H9I, respectively. Absorption spectroscopy in the vacuum ultra-violet following the flash photolysis of CH3I itself, at low pressure, demonstrates that spin orbit relaxation dominates I atom abstraction, and it is proposed that electronic deactivation is the main process for all the iodides studied. For normal and isopropyl iodides, a difference in laser action from I(52P1/2) may be attributed to the relative yields of the atoms in the 2P½ and 2P states on photodissociation rather than to any difference in the rates of electronic quenching of the excited atom by the iodides.