Surface investigations of sulphur-containing species in the interstellar medium
Wendy A. BROWN
University College London
Résumé :
Interstellar observations have identified a range of sulphur containing
species including SO, SO2, H2S, CS and OCS (amongst others). For many of
these species, gas phase chemistry accounts for the observed abundances.
However, OCS abundances cannot be reproduced by gas phase reaction
networks, and hence it is thought to be formed in the icy grain mantles
found frozen out on the surface of dust grains. With this in mind, we
have undertaken a detailed investigation of the adsorption and
desorption of OCS containing model ices on a carbonaceous dust grain
analogue surface (graphite) held at 14 K. Ultra-high vacuum techniques
have been used to model the low pressure conditions of interstellar
space and a combination of surface infrared spectroscopy and
temperature programmed desorption have been used to investigate the
thermal behaviour of the ices.
To complement our experimental studies, we have also undertaken a
computational study of the formation of OCS on a model carbonaceous
grain surface. We have investigated OCS formation via 4 different
routes. In all cases, the energetics of the formation process have been
investigated, and we have determined which reactions are most likely to
occur under the harsh conditions of the interstellar medium.
