The I(2P1/2)+O2⇄I(2P3/2)+O2(1Δ) equilibrium

The equilibrium between excited iodine atoms and oxygen has been examined by monitoring the time-dependent I*[≡I(2P1/2)] concentration following creation of this species by pulsed laser photolysis of iodine-containing precursors. A double exponential decay is observed which reflects a fast approach to equilibrium followed by a slower relaxation of the equilibrated mixture. Data obtained with the I* precursors HI and CH3I show that the rate constant for the reaction I*+O2→I+O2 is insignificant compared to that for the reaction I*+O2→I+O2(1Δ). Data obtained from the precursors i-C3F7I, n-C3F7I, C2H5I, and CF3I suggest that O2(1Δ) is rapidly relaxed by the precursor itself, by the precursor radical, or by some product formed in a reaction between the precursor radical and oxygen. The rate constant for the process I*+O2→I+O2(1Δ) has been found to be (8.8±0.9)×105 s−1 Torr−1, while that for the process I*+O2→I+O2 is (0.3±1.3)×105 s−1 Torr−1.