Time-resolved emission studies of electronically excited iodine atoms I(52P½)

Abstract

Electronically excited iodine atoms I(5²P_½) generated from the flash photolysis of CF₃I under isothermal conditions, have been monitored using the electric dipole forbidden emission I(5²P_½)→I(5²P_z.frac32)+hv(1·315µ). The high optical and collisional metastability of the excited atom, particularly in inert gases, results in the production of high concentrations of I(5²P_½), yielding adequate emission intensities, despite the low coefficient for spontaneous emission. In inert gases, the decay is controlled primarily by diffusion to the walls of the reaction vessel and thus the extrapolated rate at an infinte pressure of argon is determined by the sum of the rate of collisional quenching by the parent molecule CF₃I and that due to spontaneous emission. The characteristics of diffusion and spontaneous emission of I(5²P_½) are described. The decay of the emission has been studied in the presence of a number of added gases and the resulting quenching cross-sections compared with those obtained by time-resolved absorption spectroscopy in the vacuum ultra-violet. The experimental arrangement, designed to optimize the sensitivity to the emission at 1·315µ and the time resolution for rate measurements, is limited to the study of quenching gases whose deactivation efficiencies of I(5²P_½) are not too high. The use of this method for the study of primary processes in the photolyses of simple iodides is discussed.