Electronic Spectroscopy of Polycyclic Aromatic Hydrocarbons (PAHs) and Group IIA Metallic Oxides Open Access

Sullivan, Michael Neal (2017)

Permanent URL: https://etd.library.emory.edu/concern/etds/7p88ch32t?locale=en
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Abstract

Electronic spectroscopy is a powerful technique which can be used to elucidate the nature of bonding and structural characteristics in a variety of molecular species through the study of electronic interactions. This dissertation examines two such applications of electronic spectroscopy focusing on the study of polycyclic aromatic hydrocarbons (PAHs) and group IIA metallic oxides.

PAHs are well known to be involved in the formation of soot, affecting both the environment and human health. Two intermediate species involved in the process of PAH formation are the phenoxy and phenylperoxy radicals. These radicals were generated using an electrical discharge coupled with a supersonic expansion source. Absorption spectra were recorded using cavity ringdown spectroscopy. Molecular constants and excited state lifetimes were derived from the observed spectra. These results were supplemented using electronic structure calculations.

Group IIA metal oxides exhibit unusual bonding characteristics that are not well described by standard models. Additionally, they are also promising candidates for laser cooling experiments utilized in the generation of ultracold molecules. However detailed information on their internal state distribution required for these studies is lacking. Spectroscopic studies of three calcium oxide species are presented: CaO, CaOH, and CaOCa. Laser ablation coupled with a supersonic expansion was used to generate gas phase oxides. Emission spectra were recorded in the visible region using laser induced fluorescence spectroscopy. Molecular constants were determined from corresponding vibronic bands.

Table of Contents

List of Tables List of Figures

1. Motivation

1.1 Radical Intermediates in Soot Formation . . . . . . . . . . . . . . . 1

1.2 Candidates for Ultracold Molecules: Calcium Oxides . . . . . . . 8

2. Experimental Techniques

2.1 Cavity Ringdown Spectroscopy . . . . . . . . . . . . . . . . . . . . . . 15

2.2 Laser Induced Fluorescence . . . . . . . . . . . . . . . . . . . . . . . . 20

2.3 Supersonic Expansion . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22

3. Cavity Ringdown Spectroscopy of Polycyclic Aromatic Hydrocarbons (PAHs)

3.1 The Phenoxy Radical . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25

3.1.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28

3.1.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 32

3.1.4 Theoretical Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 34

3.1.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40

3.2 The Phenylperoxy Radical . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 45

3.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49

3.2.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . 50

3.2.4 Theoretical Calculations . . . . . . . . . . . . . . . . . . . . . . . . . 54

3.2.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

3.3 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

4. Laser Induced Fluorescence (LIF) of Calcium Metal Oxides

4.1 Calcium Oxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4.1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 65

4.1.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 67

4.1.3 Results and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . 69

4.2 Calcium Hydroxide . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76

4.2.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.2.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 79

4.2.4 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 85

4.3 Dicalcium Oxide (CaOCa) . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

4.3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 88

4.3.2 Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89

4.3.3 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91

4.3.4 Theoretical Calculations . . . . . . . . . . . . . . . . . . . . . . . . . . 95

4.3.5 Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 97

4.4 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 99

5. Concluding Remarks . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

Appendix

A. Phenoxy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 105

B. Phenylperoxy. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

C. CaOCa . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 112

Bibliography. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 113

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