Rotational Spectroscopy of O(1D) Insertion Products Open Access

Hays, Brian M. (2015)

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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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