Spectroscopic Characterization of the Low-Lying States of MX0/+ (M = Ca, Nd, Sm, Th; X = N,O) Molecules Open Access
Schmitz, Joel (Spring 2022)
Published
Abstract
Electronic structure characterization of small metal-containing molecules can determine chemical bonding properties with applications ranging to real word problems, such as safe nuclear waste treatment, to those of chemical fundamental interest, such as detangling rotational perturbations. In this work, the electronic structure of ThO, ThN, CaO, NdO0/+, and SmO0/+ was characterized through low- and high-resolution laser induced fluorescence (LIF) and dispersed fluorescence (DLIF) techniques.
The electronic structure of actinide complexes is of interest both in relation to actinide extraction in nuclear waste and the extent of 5f orbital involvement in actinide chemical bonding. Thirty-four ThO LIF transitions involving previously unobserved vibronic states were characterized, observing the Oʹ(0+) and Lʹ(1) states for the first time. Vibrationally hot spectra allowed calculation of the potential energy curve of the X1Σ+ state. Eleven vibronic transitions of ThN were observed in the range of 19,600-21,000 cm-1, determining molecular constants and fluorescence lifetimes which were complemented by electronic structure calculations.
CaO has an extremely complex excited state electronic structure, which can be explained by extreme electron localization on the Ca+ and O- centers. Higher levels of the Aʹ1Π(Xσπ-1) state (v = 10-17) were observed, as well as a perturbation of the Aʹ1Π(Xσπ-1) v = 17. DLIF spectroscopy was used to examine the homogenous perturbation of the C1Σ+( Bσσ-1) v = 7, assigning the perturbing Ω = 0+ state as the g3Π(0+)(Bσπ-1) v = 12 state.
The chemi-ionization of lanthanide metals is being employed as a method of increasing the atmospheric electron density for communication applications. Chemical launches have produced space clouds with visible emissions but spectroscopic data is lacking for cloud characterization. Molecular constants for sixteen bands of NdO as well as vibrational parameters for the X4 ground state and five low-lying excited states were determined from LIF and DLIF spectra. Molecular constants for four bands of SmO from 15,270-15420 cm-1 were determined for the 152SmO and 154SmO isotopologues. High-resolution LIF was used to observe the hyperfine structure of the [15.35]1 state and Einstein coefficients were determined from DLIF spectra. While no direct LIF observation of NdO+ or SmO+ was successful using photoionization spectroscopy, atomic and molecular fluorescence depletion was observed. Dispersed fluorescence of UV-excited gas expansions were recorded to compare to space launch results. Future work should search for NdO+ and SmO+ LIF in the near-UV range.
Table of Contents
CHAPTER 1: INTRODUCTION . 1
1.1 Introduction . 2
1.2 Chapter 1 References . 8
CHAPTER 2: EXPERIMENTAL METHODS . 10
2.1 Laser Ablation and Supersonic Expansion . 11
2.2 Laser-induced Fluorescence (LIF) . 14
2.2.1 Overview of LIF .14
2.2.2. Low-Resolution LIF Experimental Setup . 15
2.2.3. High-Resolution LIF Experimental Setup . 18
2.3. Dispersed Laser-Induced Fluorescence (DLIF) . 20
2.4 Vacuum Ultraviolet (VUV) Single-Photon Ionization . 24
2.5 Chapter 2 References . 26
CHAPTER 3: CHARACTERIZATION OF THE LOW-LYING STATES OF THO AND THN . 28
3.1. Introduction . 29
3.1.1. Motivation for Electronic Structure Characterization of Actinides . 29
3.1.2 Previous Studies of ThO . 32
3.1.3 Previous Studies of ThN . 36
3.2 ThO Results . 39
3.2.1 ThO LIF Spectra and Fitting Results . 39
3.2.2 X1Σ+ Ground State Potential Energy Curve Generation . 43
3.3 ThO Discussion . 46
3.3.1 Vibrational Extension of the C1Π, D1Π, E1Σ+, I1Π, and F1Π Electronic States . 46
3.3.2 Characterization of New Oʹ(0+) and Lʹ(1) Electronic States . 48
3.4 ThN Results . 49
3.4.1 ThN Experimental Results . 49
3.4.2 Electronic Structure Calculations. 56
3.5 ThN Discussion . 60
3.6 Chapter 3 References . 63
CHAPTER 4: PETURBATIONS OF THE Aʹ1Π(Xσπ-1) AND C1Σ+(Bσσ-1) STATES OF CAO . 71
4.1 Introduction .72
4.2 CaO Results . 76
4.2.1 The Aʹ1Π (Xσπ-1)-X1Σ+ bands . 76
4.2.2 Wavelength and Time-Resolved Fluorescence Measurements for the C1Σ+(Bσσ-1) and γ0+ States . 80
4.3 Discussion . 82
4.3.1 Aʹ1Π(Xσπ-1) v = 17 Perturbation . 82
4.3.2 Assignment of the γ0+ state as the g3Π0+ (Bσπ-1) state . 85
4.4 Chapter 4 References . 89
CHAPTER 5: CHARACTERIZATION OF THE LOW-LYING STATES OF NdO and SMO AND THE SEARCH FOR NdO+ AND SmO+ . 93
5.1 Introduction . 94
5.1.1 The Chemi-ionization of Lanthanides . 94
5.1.2 Previous Studies of NdO and NdO+ . 97
5.1.3 Previous Studies of SmO and SmO+ . 100
5.2 Preliminary NdO Results . 105
5.3 NdO+ Results . 113
5.3.1 Search for NdO+ LIF . 113
5.3.2 Emission Spectra of Nd-based Gas Expansions . 114
5.4 NdO and NdO+ Discussion . 115
5.5 SmO Results . 119
5.5.1 Low-Resolution LIF and DLIF Results . 119
5.5.2 Fluorescence Lifetime and Einstein coefficients Aij Determination . 124
5.5.3 Hyperfine Structure of the [15.35]1 State . 125
5.6 Preliminary SmO+ Results .127
5.6.1. Sm and SmO Depletion . 127
5.6.2. Emission Spectra of UV-Excited Sm-based Gas Expansions. 130
5.7 SmO and SmO+ Discussion . 131
5.8 SmO Einstein Aij Coefficients .136
5.9 Chapter 5 References . 139
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