Abstract:
Photodissociation of amorphous solid water (ASW) deposited on a thinly oxidized copper substrate at 82 K was studied by measuring O(P-3(J=2,1,0)) photoproducts detected with resonance-enhanced multiphoton ionization. For each spin-orbit state, the oxygen atom time-of-flight spectrum was measured as a function of H2O exposure, which is related to ice thickness, and 157-nm irradiation time. Four Maxwell-Boltzmann distributions with translational temperatures of 10 000 K, 1800 K, 400 K, and 82 K were found to fit the data. The most likely formation mechanisms are molecular elimination following ionization of water and ion-electron recombination, secondary recombination of hydroxyl radicals, and photodissociation of adsorbed hydroxyl radicals. Evidence for O-atom diffusion through bulk ASW was found for H2O exposures of at least 5 Langmuir (1 L = 10(-6) Torr s). The cross sections for O(P-3(2)) depletion were 1.3 x 10(-19) and 6.5 x 10(-20) cm(2) for 1 and 5 L, respectively. (C) 2014 AIP Publishing LLC.
