On the dissociation of I2 by O2(a 1Δ): Pathways involving the excited species I2(A′ Π32u,A Π31u), I2(X 1∑,υ), and O2(a 1Δ,υ)

Abstract

Kinetic studies were carried out to explore the role of the excited species I2(A′ Π32u,A Π31u), I2(X 1∑,υ), and O2(a 1Δ,υ) in the dissociation of I2 by singlet oxygen. A flow tube apparatus that utilized a chemical singlet oxygen generator was used to measure the I2 dissociation rate in O2(a 1Δ)/I2 mixtures. Vibrationally excited I2(X) is thought to be a significant intermediate in the dissociation process. Excitation probabilities (γυ) for population of the υth I2(X) vibrational level in the reaction I2(X)+I(P21/2)→I2(X,υ>10)+I(P23/2) were estimated based on a comparison of calculated populations with experimentally determined values. Satisfactory agreement with the experimental data [Barnault et al., J. Phys. IV 1, C7–647 (1991)] was achieved for total excitation probabilities partitioned in two ranges, such that Γ25≤υ≤47=∑υ=2547γυ≈0.1 and Γ15≤υ≤24=∑υ=1524γυ≈0.9. A multipathway I2 dissociation model was developed in which the intermediates are I2(A′ Π32u,A Π31u) and I2(X,υ). It was shown that the iodine dissociation process passes predominantly through the I2(A′ Π32u,A Π31u) intermediate. These states are populated by collisions of I2 with vibrationally excited O2(a 1Δ,υ) at the initiation and the chain stages, when the mole fraction of I2 is small (ηI2<1%). For higher I2 concentrations (ηI2≥1%) the excited states are populated in the chain stage by collisions of I2(X,15≤υ≤24) with O2(a 1Δ).