Photodissociation of hydrogen halides in rare gas matrices, and the effect of hydrogen bonding

Abstract

Spectra of hydrogen halides, their oligomers and complexes with the heavier rare gas atoms, xenon and krypton, and their photolysis were investigated. The monomers exhibit rotational spectra with a prominent broad R(0) line, and very sharp, weak Q(0) line. Their rotational constants are considerably lowered compared with the gas phase. The YH species hydrogen bond readily to form rigid oligomers or complexes with Xe or Kr, which in general exhibit sharp zero phonon line spectra of nonrotating molecules, with clearly resolved halogen isotopic structure. The nonrotating polymers photolyse at 193 nm more efficiently, but the YH⋯Rg complexes less efficiently than the monomers, with the photolysis of the dimers yielding BrH⋯Br “hydrogen dihalide” products. Annealing and diffusion result in formation of the HXeY rare gas compounds, and partial recovery of the YH monomers, but only very weak reformation of the (YH)n oligomers. The mechanisms of the photolysis, annealing, and diffusion processes are discussed.