Systematic Mid-IR And VUV Studies Of Electron Irradiated CO2:NH3 Interstellar Ice Analogues

James, Rachel (2020). Systematic Mid-IR And VUV Studies Of Electron Irradiated CO2:NH3 Interstellar Ice Analogues. PhD thesis The Open University.

DOI: https://doi.org/10.21954/ou.ro.00011233

Abstract

Over 200 molecules have been detected in the interstellar medium (ISM) but the formation pathways for most of these molecules remains elusive. It is now believed that a major route of molecular synthesis lies within the processing of interstellar ices formed on microscopic dust grains created in the cycle of star birth and death. However, despite decades of experimental research on molecular synthesis in ice films, the lack of a systematic approach to ISM analogue experiments means that there is still no comprehensive understanding of the influence of discrete experimental parameters on the synthesis of any molecular system under ISM conditions.

To demonstrate the advantages of performing a systematic study, this thesis presents a comprehensive analysis of thermal and electron processing of CO2:NH3 binary mixtures as a function of mixing ratio. A combination of mid-IR and VUV spectroscopy is used to identify chemical products and explore the morphology within the ice mixture demonstrating the advantages of the complementarity of the two spectroscopic methods. Mid-IR spectroscopy of the thermal processing of CO2:NH3 mixtures revealed that the ice structure is ratio dependent and that products formed by electron processing of such ices is dependent on the initial ratio of the ice. VUV spectroscopy revealed a thermal reaction which is not observed from the mid-IR spectroscopic studies and allowed new products to be identified.

This thesis therefore establishes the need to adopt a more systematic approach to ISM analogue experiments. Such comprehensive and coherent experimental data will improve the interpretation of the next generation of astrochemical observations whilst simultaneously allowing more accurate models of molecular synthesis in the ISM to be developed which in turn allows for a better understanding of processes involved in star and planet formation.

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