Astronomy and Astrophysics – Astrophysics – Galaxy Astrophysics
Scientific paper
2010-06-11
Astronomy and Astrophysics
Astrophysics
Galaxy Astrophysics
23 pages, 10 figures, accepted for publication in ApJ
Scientific paper
UV irradiation of simple ices is proposed to efficiently produce complex organic species during star- and planet-formation. Through a series of laboratory experiments, we investigate the effects of the H2O concentration, the dominant ice constituent in space, on the photochemistry of more volatile species, especially CH4, in ice mixtures. In the experiments, thin (~40 ML) ice mixtures, kept at 20-60 K, are irradiated under ultra-high vacuum conditions with a broad-band UV hydrogen discharge lamp. Photodestruction cross sections of volatile species (CH4 and NH3) and production efficiencies of new species (C2H6, C2H4, CO, H2CO, CH3OH, CH3CHO and CH3CH2OH) in water-containing ice mixtures are determined using reflection-absorption infrared spectroscopy during irradiation and during a subsequent slow warm-up. The four major effects of increasing the H2O concentration are 1) an increase of the destruction efficiency of the volatile mixture constituent by up to an order of magnitude due to a reduction of back reactions following photodissociation, 2) a shift to products rich in oxygen e.g. CH3OH and H2CO, 3) trapping of up to a factor of five more of the formed radicals in the ice and 4) a disproportional increase in the diffusion barrier for the OH radical compared to the CH3 and HCO radicals. The radical diffusion temperature dependencies are consistent with calculated H2O-radical bond strengths. All the listed effects are potentially important for the production of complex organics in H2O-rich icy grain mantles around protostars and should thus be taken into account when modeling ice chemistry.
Andersson Stefan
Linnartz Harold
Oberg Karin I.
van Dishoeck Ewine F.
No associations
LandOfFree
The effect of H2O on ice photochemistry does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.
If you have personal experience with The effect of H2O on ice photochemistry, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and The effect of H2O on ice photochemistry will most certainly appreciate the feedback.
Profile ID: LFWR-SCP-O-76838