Harpooning reactions of excited rare gas atoms

Abstract Reactive quenching of the excited states of the rare gases has been studied for more than a decade. Early, Gundel et al [J. Chem. Phys. 64,4390(1976)] proposed that reactions of the metastable states of argon (3p 5 4s[3/2] 2 and 3p 5 4s′[1/2] 0 ) were analogous to reactions of alkali metal atoms with halogens and proceeded by a harpooning mechanism, which assumes the reaction proceeds through an ion intermediary, Ar * + Cl 2 → Ar + + Cl 2 − → ArCl * + Cl. Product branching fractions, vibrational energy disposal, velocity dependence, and vibrational excitation of reactants and propensity for ion-core conservation (N. Sadeghi, in previous measurements similar to studies with copper presented in an adjacent section) have now been studied for the reactions of metastable states of all the rare gases with many chloride compounds. This paper will present recent studies of the effect of excited state energy on the harpoon reaction. We present measurements of total binary and tertiary quench rates and branching fractions for the reaction, Xe (5p 5 np,np′, n=6,7)+ Cl 2 . Xenon atoms are excited by state-selective, two-photon absorption with a u.v. laser, and the time dependent fluorescence from the excited atom in the I.R., visible, and from XeCl * (B) products near 308 nm are then measured with subnanosecond time resolution. The energy dependence of the measured reaction rates are consistent with a multichannel harpoon model to be presented which is based on the formalism of Gislason and Sachs [J. Chem. Phys. 62, 2678 (1975)].