Measurements of D 2 Yields from Amorphous D 2 O Ice by Ultraviolet Irradiation at 12 K

Abstract

We have carried out experiments on the formation of D2 molecules from amorphous D2O ice (thickness: 40, 120 Å) by UV irradiation (λ: 126, 172 nm) at 12 K. Our results show that most of the D2 products remain in and on the amorphous ice at 12 K; directly photodesorbed D2 was little observed at 12 K. The amount of D2O destruction and D2 yields after a dose of 1018 photons cm-2 at 12 K were about 10%-20% and 1%-2% of the initial number of D2O molecules, respectively. The formation reaction of D2 was found to be a single-photon process via the first excited state of D2O. The reconstruction of D2O at 12 K (reverse reaction) was not observed within our experimental timescale (5 hr). We estimated the cross sections for the D2O destruction and the D2 formation reactions by the photon impact at 12 K for the first time.