On the dissociation of $I2$ by $O2(a1Δ)$⁠: Pathways involving the excited species $I2(A′Π32u,AΠ31u)$⁠, $I2(X1∑,υ)$⁠, and $O2(a1Δ,υ)$ Available to Purchase

Kinetic studies were carried out to explore the role of the excited species $I2(A′Π32u,AΠ31u)$⁠, $I2(X1∑,υ)$⁠, and $O2(a1Δ,υ)$ 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 $O2(a1Δ)/I2$ 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 $I2(A′Π32u,AΠ31u)$ and $I2(X,υ)$⁠. It was shown that the iodine dissociation process passes predominantly through the $I2(A′Π32u,AΠ31u)$ intermediate. These states are populated by collisions of $I2$ with vibrationally excited $O2(a1Δ,υ)$ 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 $O2(a1Δ)$⁠.