HSO2 isomers in rare-gas solids

Abstract

Photochemistry of HSO₂ isomers is studied by using FTIR spectroscopy in argon, krypton and xenon solids. Photodecomposition of H₂S or H₂O was used as a hydrogen atom source to study a diffusion controlled reaction of H and SO₂. Mainly, the higher energy HSO₂ isomer is formed in this reaction which is attributed to a low barrier for the HSO₂ formation and a higher barrier for the formation of the lowest-energy species cis-HOSO. Photoexcitation of HSO₂ at wavelengths below 580 nm promotes HSO₂ → cis-HOSO interconversion. For this photoisomerisation two mechanisms are possible: direct isomerisation of HSO₂ to cis-HOSO or a cage-induced reaction. The photodissociation threshold of cis-HOSO to H + SO₂ is at 400 nm. The photon energies needed for these processes agree with the available computational data. To aid assignment of the experimental vibrational spectra, the equilibrium structures and the vibrational wavenumbers of HSO₂, trans-HOSO, cis-HOSO and HXeOSO were calculated by ab initio methods.