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Abstract: Water is abundantly present in the Universe. It is the main component ofinterstellar ice mantles and a key ingredient for life. Water in space ismainly formed through surface reactions. Three formation routes have beenproposed in the past: hydrogenation of surface O, O2, and O3. In a previouspaper Ioppolo et al., Astrophys. J., 2008, 686, 1474 we discussed anunexpected non-standard zeroth-order H2O2 production behaviour in O2hydrogenation experiments, which suggests that the proposed reaction network isnot complete, and that the reaction channels are probably more interconnectedthan previously thought. In this paper we aim to derive the full reactionscheme for O2 surface hydrogenation and to constrain the rates of theindividual reactions. This is achieved through simultaneous H-atom and O2deposition under ultra-high vacuum conditions for astronomically relevanttemperatures. Different H-O2 ratios are used to trace different stages in thehydrogenation network. The chemical changes in the forming ice are followed bymeans of reflection absorption infrared spectroscopy RAIRS. New reactionpaths are revealed as compared to previous experiments. Several reaction stepsprove to be much more efficient H + O2 or less efficient H + OH and H2 + OHthan originally thought. These are the main conclusions of this work and theextended network concluded here will have profound implications for models thatdescribe the formation of water in space.



Autor: H. M. Cuppen, S. Ioppolo, C. Romanzin, H. Linnartz

Fuente: https://arxiv.org/







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