title: Release of hydrogen molecules from the photodissociation of amorphous solid water and polycrystalline ice at 157 and 193 nm.
abstract: The production of H(2) in highly excited vibrational and rotational states (v=0-5, J=0-17) from the 157 nm photodissociation of amorphous solid water ice films at 100 K was observed directly using resonance-enhanced multiphoton ionization. Weaker signals from H(2)(v=2,3 and 4) were obtained from 157 nm photolysis of polycrystalline ice, but H(2)(v=0 and 1) populations in this case were below the detection limit. The H(2) products show two distinct formation mechanisms. Endothermic abstraction of a hydrogen atom from H(2)O by a photolytically produced H atom yields vibrationally cold H(2) products, whereas exothermic recombination of two H-atom photoproducts yields H(2) molecules with a highly excited vibrational distribution and non-Boltzmann rotational population distributions as has been predicted previously by both quantum-mechanical and molecular dynamics calculations.
authors.affiliation: Department of Molecular Engineering, Kyoto University, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yabushita
authors.forename: Tetsuya
authors.initials: T
authors.lastname: Hama
authors.forename: Daisuke
authors.initials: D
authors.lastname: Iida
authors.forename: Noboru
authors.initials: N
authors.lastname: Kawanaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Naoki
authors.initials: N
authors.lastname: Watanabe
authors.forename: Michael N R
authors.initials: MN
authors.lastname: Ashfold
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Loock