University of Sussex
Whelan, Mark Clifford.pdf (9.45 MB)

Spectroscopic studies of interstellar molecules

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posted on 2023-06-09, 06:40 authored by Mark Clifford Whelan
Astrochemistry is a wide ranging and varied field of study. Recent discoveries have highlighted the diversity of chemistry in the interstellar medium (ISM) and shown why it is worthy of significant attention. Although chemical evolution of the ISM occurs in the gas and solid phases, this work addresses solely solid phase processes using temperature programmed desorption (TPD) and reflection absorption infrared spectroscopy (RAIRS). Of particular interest is the formation and behaviour of pre-biotic molecules, such as the isomers of C2O2H6 (methyl formate, acetic acid and glycolaldehyde), which have a significant role in the formation of amino acids. Formic acid is related to the three C2O2H6 isomers and it is believed to play a role in their formation. However, studies of the behaviour of formic acid on astronomically relevant surfaces are limited. In this work, structural changes within formic acid are probed and the interaction with water, the most abundant solid phase species in interstellar ices, is examined. Both species were found to affect each other’s structural evolution in a non-trivial manner. The desorption of formic acid from water was shown to be complex and furthermore, the formic acid desorption routes were found to be highly dependent on the relative amount of formic acid present. Not only is water the most abundant species in the solid phase, it partakes in many of the processes that are responsible for the chemical complexity of the ISM. The majority of water in space is proposed to have an amorphous porous structure, called amorphous solid water (ASW), that is able to accommodate guest molecules. Structural changes within ASW trap guest molecules above their natural sublimation temperatures, increasing the opportunities available for chemical processing. Whilst the ASW to crystalline ice phase change is well documented, the initial compaction of ASW is subject to considerable debate. Differing techniques and systems yield an array of temperatures over which compaction occurs. This work compares different probe molecules and techniques when examining the compaction process. It was found, using TPD, that whilst there were some variances in the trapping of different probes, they yielded comparable compaction temperature ranges. These findings were corroborated by investigations using RAIRS. The present work makes it clear that the compaction of ASW requires substantial additional work and that comparisons between different studies that involve ASW must be carried out carefully.


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University of Sussex

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