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Rotational Spectroscopy of O(1D) Insertion Products

Hays, Brian M. (2015)
Dissertation (152 pages)
Committee Chair / Thesis Adviser: Widicus Weaver, Susanna
Committee Members: Heaven, Michael ; Lian, Tim
Research Fields: Chemistry, Physical
Keywords: Rotational Spectroscopy; Terahertz; O(1D) Insertion
Program: Laney Graduate School, Chemistry
Permanent url: http://pid.emory.edu/ark:/25593/pkcr1

Abstract

Aminomethanol (HOCH2NH2) is an important astrochemical molecule due to its proposed role in the formation of glycine, the simplest amino acid, in space. Astrochemical models have predicted aminomethanol formation in star-forming regions, but its detection in space has been precluded by its lack of a laboratory spectrum to guide astronomical searches. This molecule poses a challenge for laboratory spectroscopy because it is terrestrially unstable. The selective O(1D) insertion reaction into a C-H bond of methylamine has been proposed to create the molecule. Calculations were carried out to predict the energetics of this formation pathway, to investigate other possible products, and to predict the pure rotational spectrum of aminomethanol. To search for aminomethanol's laboratory spectrum, a new spectrometer was developed to produce molecules in the gas phase using O(1D) insertion reactions and then probe them using (sub)millimeter spectroscopy. The new experiment combined (sub)millimeter spectroscopy and a laser photolysis mixing supersonic expansion source. This experiment was first tested on the methanol and vinyl alcohol systems, produced from O(1D) insertion into methane and ethylene, respectively. Also, new fast sweeping techniques were developed to greatly increase the spectral acquisition speed of direct absorption (sub)millimeter wave spectroscopy. The fast sweeping techniques were also used to create a new (sub)millimeter - microwave double resonance spectroscopy technique. All of these techniques were then combined to aid in the search for aminomethanol. The results of these experiments as well as the current results from searches for aminomethanol are presented here.

Table of Contents

1 Introduction 1

1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1.1 Structure of the Dissertation . . . . . . . . . . . . . . . . . . . 3

2 Theoretical Calculations of O(1D) Insertion 4

2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

2.2 Theoretical Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2.3.1 Insertion Product Energetics . . . . . . . . . . . . . . . . . . . 9

2.3.2 Insertion Product Geometries . . . . . . . . . . . . . . . . . . 13

2.3.3 Prediction of Pure Rotational Spectra . . . . . . . . . . . . . 16

2.3.4 Further Predictions of the Structure of Aminomethanol . . . . 20

2.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20

3 Experimental Design 22

3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3.1.1 The insertion of O(1D) into Methane . . . . . . . . . . . . . . 23

3.2 Experimental Design and Methods . . . . . . . . . . . . . . . . . . . 23

3.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.1 Analysis Methods . . . . . . . . . . . . . . . . . . . . . . . . . 27

3.3.2 Methanol Production as a Function of Backing Pressure . . . 31

3.3.3 Methanol production as a function of laser photolysis position 32

3.3.4 Additional Reaction Products Observed . . . . . . . . . . . . 33

3.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35

4 Vinyl Alcohol 36

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 36

4.1.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . 37

4.2 Experiemental Methods . . . . . . . . . . . . . . . . . . . . . . . . . 38

4.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 40

4.3.1 Vinyl Alcohol Spectroscopy . . . . . . . . . . . . . . . . . . . 40

4.3.2 Additional Reaction Products Observed . . . . . . . . . . . . 41

4.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43

5 Fast Sweeping Direct Absorption Experiments 44

5.1 Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 44

5.2 Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 47

5.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48

5.3.1 Experimental Data . . . . . . . . . . . . . . . . . . . . . . . . 48

5.3.2 Data Analysis and Baseline subtraction . . . . . . . . . . . . . 50

5.3.3 Comparison to Previous Techniques . . . . . . . . . . . . . . . 52

5.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 54

6 Fast Sweeping Double Resonance 55

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 55

6.2 Experimental Design . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

6.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

6.3.1 Methanol double resonance . . . . . . . . . . . . . . . . . . . 59

6.3.2 Ozone double resonance . . . . . . . . . . . . . . . . . . . . . 62

6.3.3 Formaldehyde double resonance . . . . . . . . . . . . . . . . . 64

6.4 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

7 Methylamine + O(1D) 67

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

7.2 Experimental . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 68

7.2.1 Fast Sweeping Spectroscopy in a Pulsed Experiment . . . . . . 69

7.2.2 Scanning using artificially enlarged bandwidth . . . . . . . . . 73

7.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 73

7.3.1 point-by-point acquisition vs. fast sweep acquisition . . . . . . 73

7.3.2 Products Detected . . . . . . . . . . . . . . . . . . . . . . . . 75

7.4 Search for Aminomethanol . . . . . . . . . . . . . . . . . . . . . . . . 78

7.5 Conclusions and Outlook . . . . . . . . . . . . . . . . . . . . . . . . . 82

Appendix A Appendix A 85

A.1 Scripts for use of the VPT2 program in CFOUR on the Emerson Center Computing Cluster . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

A.1.1 Procedure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 86

Appendix B Appendix B 91

B.1 Supplementary Information from Hays and Widicus Weaver, 2013 . . 91

B.2 Torsional Potential Energy Surfaces . . . . . . . . . . . . . . . . . . . 92

B.3 Geometries and Vibrations . . . . . . . . . . . . . . . . . . . . . . . . 96

Appendix C Appendix C 122

C.1 Vinyl Alcohol . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

C.1.1 fit file . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 122

References 135

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