Study of Electronically Excited Iodine Atoms I(52P1/2) by Time Resolved Emission

Abstract

Donovan and Husain1–7 have recently carried out a number of investigations on electronically excited iodine and bromine atoms, I(52P1/2) and Br(42P1/2), by kinetic spectroscopy in absorption in the vacuum ultra-violet after flash photolysis of a number of gaseous halides. The long mean radiative life-times of these excited atoms8 arising out of the electric dipole forbidden transitions to the ground states, I(52P3/2) and Br(42P3/2), have facilitated such studies in absorption. This communication describes the study of the time resolved emission I(52P1/2) → I(52P3/2) + hv (1.315μ) following the flash photolysis of gaseous trifluoroiodomethane (CF3I), monitored by means of a lead sulphide photoconductive cell placed at the exit slit of a high aperture grating monochromator (Bausch and Lomb, f 4.4) and displayed on the screen of an oscilloscope. The concentrations of excited iodine atoms produced on photolysis2 are sufficiently high to overcome the low value of the Einstein coefficient for spontaneous emission, and adequate intensities are thus obtained. A typical trace for the decay of the emission is shown in Fig. 1. The decay is slower for increasing pressures of argon in accordance with a process primarily controlled by diffusion to the walls of the reaction vessel2–4.