Deactivation of excited iodine atoms I(52P½)

Abstract

Electronically excited (5p²P_½) and ground state (5p²P_z.frac32;) iodine atoms, resulting from the flash photolysis of trifluoromethyl iodide, have been monitored in absorption in the vacuum ultra-violet region of the spectrum by the method of kinetic spectroscopy. A long-lived population inversion can be observed in the absence of laser action when argon is the added gas. Under these conditions, the rate of decay of I(5²P_½) is very slow so that deactivation by other added gases can be studied conveniently, particularly as the optical transition to the ground state is electric dipole forbidden. In argon the rate of decay of the excited iodine atoms increases with decreasing pressure although the absolute magnitude of the rate is some 5-6 times that calculated according to the Chapman-Enskog equation for the diffusion of xenon in argon. For N₂ and C₃H₈, the decay exhibits first-order kinetics for these gases and is independent of the pressure of added argon. No significant contribution to the removal of I(5²P_½) by a hydrogen-atom abstraction reaction with propane was observed. No significant deactivation by CF₃I itself was observed. The collision efficiencies for the deactivation of I(5²P_½) by the gases N₂, C₃H₈ and I₂(from a previous investigation) are found to be 3.0 × 10^–6, 3.2 × 10^–4 and 7.2 × 10^–2, respectively.