FORMATION, RELAXATION AND QUENCHING OF XeF, KrF AND XeCℓ

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Abstract
Reactive quenching of the first two excited states of rare gas atoms, Rg(np5 n+1 s, 3P2 and 3P1), by halogens yields rare gas halide molecules in the B and C states and with high vibrational distributions. Interpretation of the bound-free emission spectra permits assignment of the initial distributions. Subsequent collisions of the rare gas halide molecules with He, Ne and Ar bath gas atoms result in transfer between the B and C states and vibrational relaxation. For high v levels the transfer rate is faster than vibrational relaxation, but the reverse holds for lower v levels. This can lead to a 300 K Boltzmann vibrational distribution but a nonequilibrium electronic state distribution of rare gas halide molecules in the B and C states. Modeling of the variation of the rare gas halide electronic and vibrational distributions with pressure gives a state-to-state view of relaxation processes. Photolytic dissociation of XeF2 yields XeF(B) in low v levels. Observation of the steady-state emission intensity from XeF(B), and XeF(C) from photodissociation in the presence of added reagents permits assignment of rate constants for B-C transfer and for quenching of XeF(B) and XeF(C) with 300 K Boltzmann vibrational distributions. Both the reactive quenching and photodissociation experiments indicate that the (C, Ω = 3/2) state is lower in energy than the (B, Ω = 1/2) state for XeF, XeCl and KrF. This has important implications for utilization of rare gas halide molecules for high power lasers

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