Studies of the Ices and Chiral Molecules in the Interstellar Medium Open Access

Mesko, AJ (2016)

Permanent URL: https://etd.library.emory.edu/concern/etds/ns064625v?locale=en
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Abstract

Our understanding of the chemical diversity of the interstellar
medium is ever increasing. With better observational technology
and experimentation, the detection of ices, ions, radicals,
and chiral molecules have all been conrmed. Millimeter/
submillimeter spectroscopy is one tool which has driven advances
in observational astronomy and laboratory spectroscopy.
The work presented here focuses on two experiments: the study
of interstellar ices and the study of propylene oxide, the rst
chiral molecule detected in the interstellar medium. Millimeter/
submillimeter spectroscopy is the primary technique employed
in both experiments. The premise of the interstellar
ice analogue experiment is to understand the chemical mechanisms
which can lead to the formation and desorption of key
molecules in the interstellar medium. Millimeter/submillimeter
spectroscopy allows us to study the gas phase over the surface
of the ice at high sensitivity and excellent resolution. To this
point we have studied thermal and photodesorption of water
from pure water ices, and the evolution of CO as a result of
photo-processing of pure methanol ices. The motivation of the
propylene oxide experiment is to provide new laboratory spectra
so that it can be a target for further astronomical searches.
The spectrum from 70 GHz to 1 THz is presented, the molecular
constants are determined, and the internal rotation of the
methyl group is analyzed and discussed.

Table of Contents

1 A Brief Overview of The Interstellar Environment . . . . 1
2 Rotational Spectroscopy of Gases Above Interstellar
Ice Analogues . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.1 General Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
2.2.2 Temperature Programmed Desorption of Ices . . . . . . . . . . . . 9
2.2.3 Photo-Processing of Ices . . . . . . . . . . . . . . . . . . . . . . . . 9
2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10
2.3.1 Temperature Programmed Desorption . . . . . . . . . . . . . . . . 10
2.3.2 Room Temperature gas-phase photolysis of Methanol . . . . . . . 10
2.3.3 Photodesorption of Water from an Ice Surface . . . . . . . . . . . 11
2.3.4 The Search for Methanol Photodesorption from an Ice Surface . . 12
2.3.5 Detection of Carbon Monoxide as the Result of Irradiation of
Methanol Ice . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.4 Proposed Future Work. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
2.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
3 The Millimeter/Submillimeter Spectrum of Propylene
Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 21
3.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31
A Ice Experiment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32
A.1 Temperature Programmed Desorption of Pure H2O Ices . . . . . . . . . . 32
A.2 Methanol Photolysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35
B Propylene Oxide Experiment . . . . . . . . . . . . . . . . . . . . . 37
B.1 Propylene Oxide Spectral Fitting using only V3 barrier . . . . . . . . . . 37
B.2 Propylene Oxide Spectral Assignments . . . . . . . . . . . . . . . . . . . 39
Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

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