title: Photodissociation of polycrystalline and amorphous water ice films at 157 and 193 nm.
abstract: The photodissociation dynamics of amorphous solid water (ASW) films and polycrystalline ice (PCI) films at a substrate temperature of 100 K have been investigated by analyzing the time-of-flight (TOF) mass spectra of photofragment hydrogen atoms at 157 and 193 nm. For PCI films, the TOF spectrum recorded at 157 nm could be characterized by a combination of three different (fast, medium, and slow) Maxwell-Boltzmann energy distributions, while that measured at 193 nm can be fitted in terms of solely a fast component. For ASW films, the TOF spectra measured at 157 and 193 nm were both dominated by the slow component, indicating that the photofragment H atoms are accommodated to the substrate temperature by collisions. H atom formation at 193 nm is attributed to the photodissociation of water species on the ice surface, while at 157 nm it is ascribable to a mixture of surface and bulk photodissociations. Atmospheric implications in the high latitude mesopause region of the Earth are discussed.
authors.affiliation: Department of Molecular Engineering, Kyoto University, Kyoto 615-8510, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Yabushita
authors.forename: Daichi
authors.initials: D
authors.lastname: Kanda
authors.forename: Noboru
authors.initials: N
authors.lastname: Kawanaka
authors.forename: Masahiro
authors.initials: M
authors.lastname: Kawasaki
authors.forename: Michael N R
authors.initials: MN
authors.lastname: Ashfold