Chemistry on interstellar grains and implications for infrared spectroscopy

In this article I review the infrared and millimetre-wave observations which suggest that the gas-grain interaction is important in dense clouds. This interaction results in the formation of H₂O ice in clouds having relatively low extinction. I argue that observations of the gas in hot molecular cores enables one to study grain surface processes since it appears very likely that this hot gas is rich in material evaporated from grains. The detection of large saturated molecules, such as dimethyl ether and ethanol, in such regions indicates that the surface chemistry may be very complex. Finally I discuss briefly how the unidentified infrared emission bands may be affected by chemical processes. -Author