On water formation in the interstellar medium: Laboratory study of the O+D reaction on surfaces

In the interstellar medium (ISM), an important channel of water formation is the reaction of atoms on the surface of dust grains. Here, we report on a laboratory study of the formation of water via the O+D reaction network. While prior studies were done on ices, as appropriate to the formation of water in dense clouds, we explored how water formation occurs on bare surfaces, i.e., in conditions mimicking the transition from diffuse to dense clouds (Av 1-5). Reaction products were detected during deposition and afterward when the sample is brought to a high temperature. We quantified the formation of water and intermediary products, such as D₂O₂, over a range of surface temperatures (15-25K). The detection of OD on the surface signals the importance of this reactant in the overall scheme of water formation in the ISM.