Production and loss of the water-related species H3O +, H2O and OH in dense interstellar clouds

Abstract

Following the recent determinations of the fractional abundances of H30+ and H20 in dense interstellar clouds, the production and loss processes for these species have been investigated in the laboratory. The major processes involved are dissociative electron recombination of H30+ and proton transfer to and from H20. The complete product distribution for the H30+ recombination has now been determined and leads to the product channels OH + H2(0.36), OH+2H(0.29) and 0+ H + H2(0.30) with the channel H + H20 (0.05) being much smaller than previously assumed. It has been shown that loss of H30+ by proton transfer to a series of sulphur-containing species with larger proton affinities is very efficient and also non-dissociative, further establishing the trend for proton transfer reactions involving this ion. These data have been used in a limited model to predict the fractional abundance of H20 and the relative abundances of H20 and H30+ in Sgr B2. Predictions are also made for other dense interstellar clouds.