Laboratory investigations of the role of the grain surface in astrochemical models

The rich chemistry often detected in star forming regions is now recognized to be a consequence of solid-state astrochemistry and the thermal desorption of its products. In recent experimental studies, desorption of a range of ices from a gold surface was investigated using temperature programmed desorption ( TPD). These data were then used in astrochemical models. In this paper we investigate the sensitivity of these models to the inclusion of TPD data obtained from different surfaces ( simulating different dust grains) and different thicknesses of the icy mantles. Detailed laboratory TPD studies of the desorption of ices from a highly oriented pyrolytic graphite ( HOPG) surface have been performed. Desorption temperatures and kinetic parameters have been determined directly from the TPD data and have been used to determine the expected desorption temperature for the ices from grain surfaces. The results of these experiments have been incorporated into astrochemical models of high mass star forming regions and have then been compared with the results of previous experiments. From this comparison, we are able to determine whether the nature and composition of the grain surface is important in dictating the chemistry that occurs in star forming regions.