Studies of the Ices and Chiral Molecules in the Interstellar Medium Pubblico

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

About this Master's Thesis

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School	Laney Graduate School
Department	Chemistry
Degree	MS
Submission	Master's Thesis
Language	English
Research Field	Chemistry, Physical
Parola chiave	mm/submm Spectroscopy Astrochemistry Rotational Spectroscopy
Committee Chair / Thesis Advisor	Widicus Weaver, Susanna, Emory University
Committee Members	Heaven, Michael, Emory University Evangelista, Francesco , Emory University

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