Investigation of the Role of Electronically Excited I2 in the COIL Dissociation Process

Abstract

Kinetic studies were carried out to explore the role of electronically excited iodine (I2(A′, A)) in the dissociation of I2 by singlet oxygen, and the possible role of I2+O2(b) energy transfer as the initiation step of the dissociation sequence. Flow tube measurements that utilized a chemical singlet oxygen generator were used evaluate the contribution of the O2(b)+I2 reaction. The rate of I2 dissociation was examined under conditions where varying concentrations of CO2 were used to quench O2(b). Pulsed laser pump-probe experiments were used to study the relaxation kinetics of I2(A′). The objective was to measure quenching rate constants that could be used in testing models where I2(A′) is a key dissociation intermediate. Rate constant for quenching of I2(A′) by Ar (2.7×10 cm/s), I2 (4.8×10 cm/s) and CO2 (8.5×10 cm/s) were measured. An I2 dissociation model in which the electronically excited intermediate I2(A′ or A) is populated by collisions with vibrationally excited O2(a) was found to be in good agreement with experiment.