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

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 exhibi t sharp zero phonon line spectra of nonrotating molecules, with clearly res olved 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 photolysi s, annealing, and diffusion processes are discussed. (C) 2000 American Inst itute of Physics. [S0021-9606(00)00701-7].