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 I(2)(A(') (3)Pi(2u),A (3)Pi(1u)), I(2)(X (1) summation operator,upsilon), and O(2)(a (1)Delta,upsilon) in the dissociation of I(2) by singlet oxygen. A flow tube apparatus that utilized a chemical singlet oxygen generator was used to measure the I(2) dissociation rate in O(2)(a (1)Delta)/I(2) mixtures. Vibrationally excited I(2)(X) is thought to be a significant intermediate in the dissociation process. Excitation probabilities (gamma(upsilon)) for population of the upsilonth I(2)(X) vibrational level in the reaction I(2)(X)+I((2)P(1/2))-->I(2)(X,upsilon>10)+I((2)P(3/2)) 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 Gamma(25</=upsilon</=47)= summation operator(upsilon=25) (47)gamma(upsilon) approximately 0.1 and Gamma(15</=upsilon</=24)= summation operator(upsilon=15) (24)gamma(upsilon) approximately 0.9. A multipathway I(2) dissociation model was developed in which the intermediates are I(2)(A(') (3)Pi(2u),A (3)Pi(1u)) and I(2)(X,upsilon). It was shown that the iodine dissociation process passes predominantly through the I(2)(A(') (3)Pi(2u),A (3)Pi(1u)) intermediate. These states are populated by collisions of I(2) with vibrationally excited O(2)(a (1)Delta,upsilon) at the initiation and the chain stages, when the mole fraction of I(2) is small (eta(I(2) )<1%). For higher I(2) concentrations (eta(I(2) )>/=1%) the excited states are populated in the chain stage by collisions of I(2)(X,15</=upsilon</=24) with O(2)(a (1)Delta).