Photofragmentation dynamics and reactive collisions of laser-excited electronic states

Abstract

Tunable laser excitation followed by observation of infrared fluorescence provides a means of readily studying electronically excited photoproducts and their reactions. A number of specific examples involving the production of I*(5²P_1/2) and Br*(4²P_1/2) upon molecular photodissociation are considered. The quantum yield of I* production from HgI₂ is obtained as a function of wavelength. An inconclusive search was made for unobserved states in IBr which lead to I* product atoms and for states of BrCl which lead to Br*. Photodissociation of CH₂I₂ in an intense laser field is observed to undergo multiphoton dissociation. Quenching and reactive collisions of Br* and I* with halogens, I₂, Br₂ and Cl₂, and interhalogens, IBr, ICl and BrCl, are investigated. Electronically adiabatic reactive channels are detected for the collisions I*+ Br₂→ IBr + Br* and I*+ IBr → I²+ Br*. Vibrationally excited HBr product molecules are observed in 10% of the quenching collisions of Br* with H₂S.