Studies of interstellar surface chemistry: experiment and theory

Ayling, Sean Antony (2019) Studies of interstellar surface chemistry: experiment and theory. Doctoral thesis (PhD), University of Sussex.

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Astronomers seek information about the interactions occurring between complex organic molecules (COMs) and other common interstellar species. This information can help in understanding the conditions during star formation, and it is possible that this interstellar chemistry primes developing planetary systems with some of the essential compounds involved in the chemistry of life. Due to the conditions in interstellar space, the effects of particle bombardment, thermal processing and ultraviolet irradiation must be considered.

Laboratory surface science and theoretical modelling are employed because about 1 % of the mass of the interstellar medium (ISM) is in the form of dust grain particles, and these are considered to play an essential role in interstellar chemistry. In the experimental work, thin-layer ices of three COMs (2-propanol, dimethyl ether and acetaldehyde) were studied on a graphite surface, which served as the analogue for a carbonaceous dust grain, at ultra-high vacuum pressures and cryogenic temperatures. Observations of the ices were made via mass spectrometry and infrared spectroscopy. For the theoretical work, a number of adsorbing molecules were studied, and both cluster and periodic models of a graphite surface were considered.

Data for pure COM ices on graphite provided a reference point when observing more complex phenomena such as those COMs interacting with adsorbed water layers, and was also used to benchmark theoretical results. The amorphous-crystalline phase change of water was inhibited by the presence of 2-propanol, and this would be expected to affect the trapping and release of volatile chemical species in the ISM. Dimethyl ether and acetaldehyde had minimal effect on the water phase change, and showed broadly similar desorption from layered and mixed ices. Lastly, the theoretical model was established as consistently describing physisorption for a range of COMs on graphite

Item Type: Thesis (Doctoral)
Schools and Departments: School of Life Sciences > Chemistry
Subjects: Q Science > QB Astronomy > QB0495 Descriptive astronomy > QB0799 Stars > QB0806 Stellar evolution
Depositing User: Library Cataloguing
Date Deposited: 28 Jun 2019 08:40
Last Modified: 27 Jul 2022 08:55

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