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Spectroscopic Characterization of Matrix Isolated Transient Species

Lue, Christopher James (2008)
Dissertation (182 pages)
Committee Chair / Thesis Adviser: Heaven, Michael
Committee Members: Lian, Tim ; Kaufman, Myron J ;
Research Fields: Chemistry, Physical
Keywords: Heavy Metals; Actinides; Matrix Isolation; Spectroscopy; Electronic Spectroscopy; Rare Gas Radical;
Program: Laney Graduate School, Chemistry
Permanent url: http://pid.emory.edu/ark:/25593/16vh3

Abstract

Part I describes the electronic spectra of various actinide containing compounds isolated

in solid Ar using laser induced fluorescence (LIF) spectroscopy. The IR spectra

for many of the same molecules were also recorded to aid in the identification of the

fluorescing species in the LIF spectra.

LIF spectra of UO 2 isolated in solid Ar were recorded to investigate the interactions

between actinide compounds and the rare gas matrix host. At the time of the

experiments, it had been proposed that for UO 2 and CUO , the interactions between

the actinide containing molecule and Ar were strong enough to reorder the low-lying

electronic states of the molecule. The experiments presented here showed no evidence

of a reordering of low-lying electronic states based on comparison of the matrix spectra

with theoretical predictions and gas phase spectra. An attempt to observe fluorescence

from higher order uranium oxides also was undertaken.

LIF and IR spectra of thermally vaporized UCl4 isolated in solid Ar were recorded.

UCl 4 contains U(IV), which is the most stable oxidation state other than U(VI).

Before these experiments, no fluorescence had been recorded that could be attributed

to UCl 4 . Based on the observed vibrational frequencies in the fluorescence bands and

the lifetime of the fluorescence, it was determine that there was at least two different

fluorescing species. A low resolution map for the electronic levels in UOCl x was created.

Additionally, the LIF spectra of UFx (uranium fluoride fragments) and UN2 was undertaken.

The UN2 experiments were interesting because they showed the formation of U atom clusters.

The final part of this thesis focuses on the electronic spectra of Xe-OH isolated

solid Ar. Rare gas radical systems (Rg-X) such as Rg-OH are a good model system

for studying weak, long range intermolecular interactions. It is known that when

Rg=Xe, the strength of the interaction is much larger. For most Rg-OH complexes,

the spectroscopic constants have been determined previously[3]. However, the constants

for Xe-OH ares currently undetermined. Gas-phase studies were undertaken to

determined these constants.[4] With ambiguities in the gas-phase spectra, the

matrix isolation experiments described here were preformed.

Table of Contents

Contents

1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

1.1 Actinide Spectroscopy . . . . . . . . . . . . . . . . . . . . . . . 2

1.2 Rare Gas Radical Complexes . . . . . . . . . . . . . . . . . . . 3

2 Introduction to Matrix Isolation Spectroscopy . . . . . . . . . 5

2.1 Why is Matrix Isolation Spectroscopy Useful? . . . . . . . . 5

2.2 Experiment Setup . . . . . . . . . . . . . . . . . . . . . . . . . . 7

2.3 Sample Preparation . . . . . . . . . . . . . . . . . . . . . . . . 11

2.3.1 Room Temperature Gaseous Samples . . . . . . . . . . . 12

2.3.1.1 Cl 2 Shakedown Experiments . . . . . . . . . . . . . . . . 13

2.3.1.2 Using a Microwave Discharge to Fragment Samples

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

2.3.2 Room Temperature Solid Samples . . . . . . . . . . . . . 16

2.3.2.1 Laser Ablation . . . . . . . . . . . . . . . . . . . . . . . . . 16

2.3.2.2 Thermal Processes . . . . . . . . . . . . . . . . . . . . . . 20

2.4 Data Collection and Processing . . . . . . . . . . . . . . . . 21

I Electronic and Infrared Spectra of Actinide Compounds

Isolated in Solid Ar . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

3 Introduction to Actinide Spectroscopy . . . . . . . . . . . . . 25

3.1 Interests in Actinide Spectroscopy . . . . . . . . . . . . . . 25

3.2 Theoretical Treatment of Actinides . . . . . . . . . . . . . . 29

3.2.1 Ligand Field Theory. . . . . . . . . . . . . . . . . . . . . . . 29

3.2.2 Other Theoretical Approaches . . . . . . . . . . . . . . . . 34

3.3 Matrix Effects in Heavy-Metal Spectroscopy . . . . . . . . 37

4 Uranium Dioxide (UO 2 ) . . . . . . . . . . . . . . . . . . . . . . 39

4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39

4.2 Experiment Details . . . . . . . . . . . . . . . . . . . . . . . . . 41

4.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42

4.3.1 Fixed Wavelength Excitation . . . . . . . . . . . . . . . . . 42

4.3.2 Tunable Wavelength Excitation . . . . . . . . . . . . . . . . 44

4.4 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . 45

4.4.1 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 56

5 Uranium Chlorides . . . . . . . . . . . . . . . . . . . . . . . . . . . 58

5.1 UCl 4 and Its Chemical, Physical, and Spectra Properties

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 59

5.2 Experiment Details . . . . . . . . . . . . . . . . . . . . . . . . . . 60

5.3 The Uranyl Ion and the Oxidation of UCl 4 to Form UO 2 Cl 2

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63

5.4 Further Experiments . . . . . . . . . . . . . . . . . . . . . . . . . 64

5.4.1 IR Absorption Spectra . . . . . . . . . . . . . . . . . . . . . . . 64

5.4.2 Fixed Frequency Excitation . . . . . . . . . . . . . . . . . . . . 65

5.4.3 Tunable Excitation . . . . . . . . . . . . . . .. . . . . . . . . . . 68

5.5 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . 70

5.5.1 Long-Lived Fluorescence . . . . . . . . . . . . . . . . . . . . . 70

5.5.2 Short-Lived Fluorescence . . . . . . . . . . . . . . . . . . . . . 78

5.6 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80

6 UO 3 and Higher Order Oxides . . . . . . . . . . . . . . . . . . . . 81

6.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81

6.2 Experiment Details . . . . . . . . . . . . . . . . . . . . . . . .. . . 83

6.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 84

6.3.1 Infrared Absorption Spectra . . . . . . . . . . . . . . . . . . . 84

6.3.2 Fixed Wavelength Excitation . . . . . . . . . . . . . . . . . . . 86

6.3.3 Tunable Excitation . . . . . . . . . . . . . . . . . . . . . . . . . 88

6.4 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . 90

6.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 94

7 Uranium Fluorides . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

7.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96

7.2 Experiment Details . . . . . . . . . . . . . . . . . . . . . . . . . . 98

7.2.1 Formation of UF x by Passing UF 6 through a Microwave Discharge.

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 98

7.2.1.1 Preliminary Spectra of UF 6 . . . . . . . . . . . . . . . . . . . 99

7.2.2 Formation of UF x by Mixing Ablated U with F 2 . . . . . . . 102

7.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 102

7.3.1 Spectra for UF x Products Generated by Passing UF 6 through

a Microwave Discharge. . . . . . . . . . . . . . . . . . . . . . . . . . 102

7.3.1.1 Fixed Frequency Excitation . . . . . . . . . . . . . . . . . . 102

7.3.1.2 Tunable Excitation . . . . . . . . . . . . . . . . . . . . . . . . 104

7.3.2 Spectra from the Formation of UF x by Mixing Ablated U with

F 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 107

7.3.2.1 Fixed Frequency Excitation . . . . . . . . . . . . . . . . . . . 107

7.3.2.2 Tunable Excitation . . . . . . . . . . . . . . . . . . . . . . . . 107

7.4 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . 109

7.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .112

8 The Search for the Electronic Spectra of Uranium Nitrides

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

8.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 114

8.2 Experiment Details . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

8.2.1 IR Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 116

8.2.2 Fixed Frequency Excitation . . . . . . . . . . . . . . . . . . . . . 119

8.2.2.1 Tunable Excitation . . . . . . . . . . . . . . . . . . . . . . . . . 119

8.2.3 Visible Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 125

8.3 Determining the Fluorescing Species . . . . . . . . . . . . . . . . 126

8.4 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . . 129

8.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 131

II Electronic and Infrared Spectroscopy of OH-Xe Isolated

in Solid Ar . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133
9 OH-Xe . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

9.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134

9.2 Experiment Details Generating OH and Xe-OH . . . . . . . . . . 140

9.3 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

9.3.1 IR Spectra . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 141

9.3.2 Fixed Frequency Excitation . . . . . . . . . . . . . . . . . . . . . . 142

9.3.3 Tunable Excitation . . . . . . . . . . . . . . . . . . . . . . . . . . . 145

9.4 Analysis and Discussion . . . . . . . . . . . . . . . . . . . . . . . . . 146

9.5 Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .150

A A Note About Actinide Radioactivity. . . . . . . . . . . . . . . . . . .151

B The Synthesis of Uranium Chloride . . . . . . . . . . . . . . . . . . 152

Bibliography . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 154

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