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.

Formation mechanisms of oxygen atoms in the O(D21) state from the 157nm photoirradiation of amorphous water ice at 90K

“…Following the ultraviolet photolysis of H 2 O 2 in various rare-gas matrices at 7.5 K, a ͑H 2 O-O͒ complex was formed from the recombination of OH radicals, while the primary formations of H 2 O+O͑ 1 D͒ or O͑ 3 P J ͒ have not been established from the photodissociation of gaseous H 2 O 2 at 124-254 nm. 11,12 Experimental works on photon-or electron-stimulated desorption ͑ESD͒ of species from water ice have also been reported, [13][14][15][16][17][18][19][20] In the present study, using pulsed 157 nm ͑181 kcal/ mol͒ laser radiation the desorptions of electronically excited O͑ 1 D͒ atoms via the primary and secondary photoprocesses from ASW at 90 K have been directly confirmed by REMPI. Translationally and internally excited OH formation mechanisms were also discussed since hot OH is a plausible source for the oxygen atom.…”

Formation mechanisms of oxygen atoms in the O(PJ3) state from the 157nm photoirradiation of amorphous water ice at 90K

“…10 The primary formations of H 2 O+O͑ 1 D 2 ͒ or O͑ 3 P J ͒ were not established in the photodissociation of gaseous H 2 O 2 at 124-254 nm. 11 It has not been confirmed whether reaction ͑4͒ occurs in the condensed phase photolysis of water ice.…”

“…[29][30][31] Following the ultraviolet photolysis of H 2 O 2 in various rare-gas matrices at 7.5 K, the complex, ͑H 2 O-O͒, was formed from the recombination reaction of OH photoproducts. 10 where the notation "ads" stands for condensed phase or adsorbed state, and the thermodynamic data for adsorbed species are taken from those for the solid phase. The notation "i" stands for species at the ASW/vacuum interface, and for these species we use the gas phase thermodynamics data.…”

Radical Photochemistry in Oxygen‐Loaded Ices

“…[30,31] Atomic oxygen in particular has already been mentioned as coexisting with water ice through formation of the complex H 2 O·O. [32] The structure observed at 532.6 eV (peak 6) corresponds to hydrogen peroxide (H 2 O 2 ). [33] To the best of our knowledge, the species giving rise to peak 3 at 528.5 eV has not been characterized yet.…”