Direct observation of I2 collisional dissociation by O2(b1Σ+g)

Abstract
Collisional dissociation of I2 by O2(1J) has been directly observed by monitoring the appearance rate and amplitude of transient I(5 2P3/2) absorption on the 6 2P3/2‐5 2P3/2 resonance line at 178 nm. A pulsed, Raman‐shifted dye laser was used to excite a single rotational line of O2(1J, v′ = 0) near 763 nm. Radiation at this wavelength also dissociated some I2 via absorption to the continuum region of the I2(A 3R1u) state. The variation in the appearance rate of the iodine atom signal with I2 pressure leads to a rate constant for total deactivation of O2(1J) by I2 of k = 7×10−11 cm3 molecules−1 sec−1. Comparison of the amplitude of the I‐atom absorption signal induced by O2(1J) dissociation of I2 to that resulting from direct I2 photodissociation leads to the conclusion that the branching ratio for O2(1J)+I2→O2+2 I versus all other pathways is less than 0.2.