Chemistry and infrared spectroscopy of interstellar grains

This thesis focuses on three aspects of interstellar grains: the photochemistry of the grain mantles, their infrared spectroscopy and the surface chemistry that takes place during mantle accretion. It provides a combination of pure and applied chemistry and spectroscopy. The experiments described in this thesis have been carried out with low temperature (10 K) solid molecular mixtures representing the mantles of interstellar grains. The samples have been prepared by slowly condensing gaseous mixtures of simple molecules (e.g. CO, H2O, NH3, CH4) on a cold substrate (mirror or window) cooled by a cryogenic refrigerator mounted in a high vacuum chamber. Fourier transform infrared spectroscopy has been used to study the sample. A laboratory study of the photochemistry in interstellar grain mantles is described. It shows that irradiation of solid binary mixtures of CO with H2O, NH3 or CH4 with 1600 A vacuum ultraviolet light, which is representative of the interstellar ultraviolet field, gives rise to the formation of a number of large molecules as well as radicals. Moreover, a theoretical study is given of the chemical composition of grain mantles accreted in dense clouds. (Auth.)