Spectroscopic Characterization of Matrix Isolated Transient Species Open Access
Lue, Christopher James (2008)
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 . . . . . . . . . . . . . . . . . . . . . . . . . . . 243 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 . . . . . . . . . . . . . . . . . . . . . . . 705.5.1 Long-Lived Fluorescence . . . . . . . . . . . . . . . . . . . . . 70
5.5.2 Short-Lived Fluorescence . . . . . . . . . . . . . . . . . . . . . 785.6 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 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1349.1 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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