Jean-Christophe Loison, Philippe Halvick, Astrid Bergeat, Kevin M. Hickson, Valentine Wakelam
The association reaction S + CO {\to} OCS + hnu has been identified as being
particularly important for the prediction of gas-phase OCS abundances by
chemical models of dark clouds. We performed detailed ab-initio calculations
for this process in addition to undertaking an extensive review of the
neutral-neutral reactions involving this species which might be important in
such environments. The rate constant for this association reaction was
estimated to be several orders of magnitude smaller than the one present in
current astrochemical databases. The new rate for this reaction and the
introduction of other processes, notably OH + CS {\to} OCS + H and C + OCS
{\to} CO + CS, dramatically changes the OCS gas-phase abundance predicted by
chemical models for dark clouds. The disagreement with observations in TMC-1
(CP) and L134N (N), suggests that OCS may be formed on grain surfaces as is the
case for methanol. The observation of solid OCS on interstellar ices supports
this hypothesis.
View original:
http://arxiv.org/abs/1201.4256
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