open access

https://hdl.handle.net/2115/34705

Release of hot hydrogen molecules from vacuum ultraviolet photodissociation of water ice : atomospheric and astrophysical implications

日本語

2008-03-31

北海道大学低温科学研究所

Low Temperature Science

66

23-30

1章 分子雲における氷と低温化学過程

The formation mechanisms of molecular hydrogen by ultraviolet photolysis of water ice and the importance of vibrationally excited H2 to atmospheric and astrophysical chemistry are reviewed. There are two important candidates for molecular hydrogen formation from the photodissociation of H2O + hv → H + OH, that is, H + H2O → H2 + OH (abstraction reaction) and H + H → H2 (recombination reaction). The abstraction reaction is 0.6 eV endothermic, and it can proceed for energetic H atoms above the threshold energy of 1 eV (c.m.). The recombination reaction can produce the H2 molecule on ice surface, and is 4.5 eV exothermic. Using quantum state-elective detection of the H2 photoproduct, two mechanisms were characterized by which molecular hydrogen is formed following 157 nm photodissociation of amorphous water ice at 100 K. Abstraction of a hydrogen atom from H2O by the photolytically produced H-atom is observed to lead to internally "cold" H2 products, whereas recombination of two hydrogen atoms is observed to produce internally "hot" H2. The formation of vibrationally excited H2 products following photodissociation of ice could thus lead to a significant acceleration of oxygen chemistry in the interstellar medium.

紀要論文

Version of Record

1880-7593