The Study of Interstellar Ice Analogues 公开

Smith, Houston (Spring 2018)

Permanent URL: https://etd.library.emory.edu/concern/etds/7w62f8209?locale=zh
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Abstract

The interstellar medium is an environment that has harsh conditions which can lead to chemical complexity and diversity. Within the interstellar medium, cold molecular cores exist where molecules are both in the gas phase and frozen out on to carbonaceous or silicate grains. Reactions on these grains have been proposed to be a main pathway for the formation of both water and methanol. Methanol has also been proposed to be a starting point for the creation of organic molecules that are biologically relevant, such as amino acids, in an interstellar environment. This work focuses on using mm/sub-mm spectroscopy as a novel technique to detect desorbed molecules from either a thermally processed and/or photoprocessed interstellar ice analogue. The thermal desorption and photofragmentation of methanol were studied, and the results are discussed with a comparison to literature values. The thermal desorption of methanol is approximately 20 K higher than literature values while CO, a desorbed photofragment of a methanol ice, was observed at much higher temperatures than literature values. These temperature discrepancies are discussed within this work. The improvement and optimization of the spectrometer design was completed with the aim of doubling the signal-to-noise (S/N) ratio. However, similar S/N ratios were observed, so further optimization of the spectrometer is needed. When optimized, the increase in S/N ratio will hopefully give more insight into the temperature discrepancies seen from literature values in the thermal processing and photoprocessing of a methanol ice.

Table of Contents

 

 

Table of Contents

1 – Introduction.............................................................................................................................(1) 

2 – Experimental Methods............................................................................................................(6) 

3 – Results and Discussion.........................................................................................................(11) 

4 – Conclusion............................................................................................................................(25)

Figures

1 – Schematic of an interstellar ice grain.....................................................................................(2)

2 – Single-pass frequency-modulated schematic........................................................................(7) 

3 – Side view of both spectrometer designs................................................................................(7) 

4 – Diagram of VDI multiplier chain arrangement capabilities.....................................................(8) 

5 – Double-pass frequency-modulated schematic.....................................................................(10) 

6 – S/N ratio comparison for QFI/2BI and QNbB/PTC Bolometers............................................(13) 

7 – Methanol thermal Desorption...............................................................................................(15)

8 – Water contamination in methanol photolysis........................................................................(17) 

9 – CO desorbed photoproduct of methanol ice.........................................................................(19)

10 – Further water contamination in methanol photolysis..........................................................(21)

11 – Gas phase water pressure sensitivity.................................................................................(22)

12 – Water S/N ratio comparison for spectrometer designs.......................................................(23)

Tables 

1 – S/N ratio for four CH3OH lines for the QNbB/PTC and QFI/2BI Bolometers .......................(14)

 

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