Puletti, F; (2014) Laboratory spectroscopic studies of interstellar ice analogues. Doctoral thesis , UCL (University College London).

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Abstract

In recent years, the molecular chemistry in interstellar environments has proven to be far more complex than was initially expected. We live in a molecular universe that is rich with molecules formed both in the gas phase and on the surface of interstellar icy dust grains. Two important classes of interstellar molecules are sulphur-bearing species and complex organic molecules, i.e., molecules containing carbon and containing more than 6 atoms. The former are relevant because of their potential utility in establishing the age of star forming regions. The latter are important because they are excellent probes of the physical conditions of the regions where they reside. Moreover, complex organic molecules are thought to be astrobiologically relevant. To properly understand the chemical networks leading to the formation of astrochemical species, to date more than 170 have been conclusively identified, the integration of laboratory experimental data with existing computational models is paramount. Laboratory studies can be conducted in the gas phase or, as is the case for this work, in the solid state. Studies of the processing of ices, by thermal energy or by ultraviolet radiation, are particularly important in understanding solid phase chemistry in the interstellar medium. In this thesis, the results of laboratory experiments aiming to mimic the physical/chemical reactions of ices on interstellar dust grains are presented. Specifically, temperature programmed desorption and reflection absorption infrared studies were carried out in an ultra high vacuum setup on H2S (chapter 3) and on the C2H4O2 isomer family (chapters 4 and 5) formed of acetic acid (CH3COOH), glycolaldehyde (HOCH2CHO) and methyl formate (HCOOCH3). Ultraviolet irradiation studies of glycolaldehyde have also been performed, and the results of these are presented in chapter 6. In order to put the laboratory results into an astrophysical context, computer simulations of the desorption of these species from interstellar grains were conducted. The results for H2S are presented in chapter 3. Those for acetic acid, glycolaldehyde and methyl formate are presented in chapter 4.

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