Simultaneous Hydrogenation and UV-photolysis Experiments of NO in
  CO-rich Interstellar Ice Analogues; linking HNCO, OCN-, NH2CHO and NH2OH
  The laboratory work presented here, simulates the chemistry on icy dust
grains as typical for the 'CO freeze-out stage' in dark molecular clouds. It
differs from previous studies in that solid-state hydrogenation and vacuum
UV-photoprocessing are applied simultaneously to co-depositing molecules. In
parallel, the reactions at play are described for fully characterized
laboratory conditions. The focus is on the formation of molecules containing
both carbon and nitrogen atoms, starting with NO in CO-, H2CO-, and CH3OH-rich
ices at 13 K. The experiments yield three important conclusions. 1. Without
UV-processing hydroxylamine (NH2OH) is formed, as reported previously. 2. With
UV-processing (energetic) NH2 is formed through photodissociation of NH2OH.
This radical is key in the formation of species with an N-C bond. 3. The
formation of three N-C bearing species, HNCO, OCN- and NH2CHO is observed. The
experiments put a clear chemical link between these species; OCN- is found to
be a direct derivative of HNCO and the latter is shown to have the same
precursor as formamide (NH2CHO). Moreover, the addition of VUV competing
channels decreases the amount of NO molecules converted into NH2OH by at least
one order of magnitude. Consequently, this decrease in NH2OH formation yield
directly influences the amount of NO molecules that can be converted into HNCO,
OCN- and NH2CHO.
