Formation mechanisms of oxygen atoms in the O(D-1(2)) state from the 157 nm photoirradiation of amorphous water ice at 90 K

Abstract

Vacuum ultraviolet photolysis of water ice in the first absorption band was studied at 157 nm. Translational and internal energy distributions of the desorbed species, O(1D) and OH(v = 0, 1), were directly measured with resonance-enhanced multiphoton ionization method. Two different mechanisms are discussed for desorption of electronically excited O(1D) atoms from the ice surface. One is unimolecular dissociation of H2O to H2+O(1D) as a primary photoprocess. The other is the surface recombination reaction of hot OH radicals that are produced from photodissociation of hydrogen peroxide as a secondary photoprocess. H2O2 is one of the major photoproducts in the vacuum ultraviolet photolysis of water ice.