Photochemistry of hydrogen peroxide in Kr and Xe matrixes

Abstract

UV photolysis of hydrogen peroxide (H2O2) in various rare-gas matrixes is comparatively studied. The photorecovery of H2O2 from the tight H2O⋯O complex is observed in Kr and Xe matrixes, in addition to this reaction in an Ar matrix found previously. The similarity of spectral position and efficiency of the photorecovery reaction in various rare-gas solids indicates its fundamental character, supports charge-transfer excitation of H2O⋯O as its origin, and preserves promises to find this photoreaction in media of environmental importance. In UV photolysis of H2O2, the relatively small concentration of isolated OH radicals is found in a Kr matrix, and no OH radicals appear in a Xe matrix, and this trend is discussed in terms of delayed cage exit. Moreover, additional species photogenerated from H2O2 in a Xe matrix as well as the absence of OH radicals might be connected with participation of some hidden intermediates (HOXeOH, HXeOOH, etc.) in the dynamics, thus, catalyzing new photodissociation channels. Among the photolysis products, the loose H2O//O complex is suggested to be stabilized in Kr and Xe matrixes. This loosely bound complex is quasistable and decomposes at relatively low temperatures (below 20 K) quantitatively forming the known tight H2O⋯O structure. This low-temperature process offers one additional example of short-range atomic mobility introduced recently in the literature.