From interstellar carbon monosulfide to methyl mercaptan: paths of least
  resistance
  The 29 reactions linking carbon monosulfide (CS) to methyl mercaptan (CH3SH)
via ten intermediate radicals and molecules have been characterized with
relevance to surface chemistry in cold interstellar ices. More intermediate
species than previously considered are found likely to be present in these
ices, such as trans- and cis-HCSH. Both activation and reaction energies have
been calculated, along with low-temperature (T > 45~K) rate constants for the
radical-neutral reactions. For barrierless radical-radical reactions on the
other hand, branching ratios have been determined. The combination of these two
sets of information provides, for the first time, quantitative information on
the full H + CS reaction network. Early on in this network, that is, early on
in the lifetime of an interstellar cloud, HCS is the main radical, while later
on this becomes first CH2SH and finally CH3S.
