Temperature dependence of collisionally induced spin orbit relaxation of electronically excited iodine atoms, I(5 5p2P½)

Abstract

The temperature dependence of the spin orbit relaxation of electronically excited iodine atoms, I(5²P_½), has been investigated in the temperature range 180–410 K. I(5²P_½) was generated by pulsed irradiation of CF₃I and monitored photoelectrically, in the presence of various collision partners, by atomic absorption spectroscopy using attenuation of resonance radiation. Rate constants for the deactivation of the exicted atom are reported for the following molecules: H₂, D₂, N₂, O₂, CO, NO, I₂, CH₄, C₂H₂, C₂H₄, C₂H₆, C₃H₈, n-C₄H₁₀ and CH₃—CHCH₂. In general, a small variation of the rate of quenching is observed over the temperature range, together with low Arrhenius A factors, consistent with the effects of “non-adiabatic transitions” from one potential energy surface to another. The rate of quenching by molecular iodine itself, gave rise to a clear negative temperature dependence, indicative of strong bonding in the collision complex. The data for N₂ and CO gave good agreement with theoretical calculations of Nikitin based on a weak interaction on collision and electronic to vibrational energy transfer.