Understanding the chemistry of beryllium using photoelectron velocity map imaging spectroscopy Público
Green, Mallory (Spring 2020)
Abstract
Contrary to its small size, beryllium has been known to participate in anomalous bonding, which disregards periodic trends and can present numerous theoretical challenges. Due to toxicity concerns, experimental study of beryllium has historically been avoided. However, here we present the use of a photoelectron velocity map imaging spectrometer, used to provide new information about previously unexplored beryllium containing anions. For all anions studied, neutral electron affinities and anion spectroscopic constants were established and the experimental results were found to be in good agreement with our ab initio calculations.
Each of the species described, herein, exhibited unusual bonding behavior, expected of beryllium species: BeO- and BeS- were found to sustain a dipole bound excited state, a state where the parent molecule experiences long range attractions to the departing electron, to form a bound state 100-200 cm-1 below the threshold of electron detachment. The BeF- anion demonstrated beryllium’s Lewis acidity and ability to participate in closed shell bonding, as the strong dative bond (D0- > 28460 cm-) between Be (1S0) and F- (1S0) was found to be supported by back donation of electron density from the F- to the Be. Also, the confirmation of the ground state geometry of BeC2 and BeC2- (T-shaped) demonstrated propensity for covalent bonding of beryllium, even as a metal, as the bond between the Be and C2 subunit, in both molecules, was found to be polar covalent with strong electrostatic contributions.
Other small beryllium containing anions, as well as, thorium oxide clusters (ThnOm-) were explored using our velocity map instrument. However, resolved spectra could not be obtained for these species. Indications of hot source conditions, are believed to be hindering the elucidation of spectra for more electronically complicated species. Inclusion of a cold trap to the instrument will improve resolution for these species, as well as pave the way for studying Ben and Ben- clusters.
Table of Contents
CHAPTER 1: INTRODUCTION………………………………………………….……...................................................……… 1
1.1 The Chemistry of Beryllium ……………………………………………………...................................................….…... 2
1.2 Advent of Photoelectron Velocity Map Imaging Spectroscopy…………...................................................………. 8
1.3 Chapter 1 References……………………………………………………………..…......................................................... 15
CHAPTER 2: EXPERIMENTAL METHODS……….………………………….……..................................................…..… 21
2.1 Experimental Overview …………………………………………………................................................................…... 22
2.2 Laser Ablation………………………………………………………………...................................................…….…........ 24
2.3 Mass Separation……………………………………………………………....................................................…....…....... 27
2.4 Molecular Packet Guiding ……………………………………………............................................................…...…... 31
2.5 Photodetachment and Velocity Map Imaging ……………………..…..................................................……...…... 32
2.6 Detecting and Recording Electron Distributions ……………….....................................................…………....... 35
2.7 Image Reconstruction……………………………………………..……..................................................……...……..... 37
2.8 VMI Calibration………………………………………………..………..................................................……...……........ 39
2.9 Chapter 2 References………………………………………….…………..................................................……….…...... 42
CHAPTER 3: PHOTODETACHMENT SPECTROSCOPY OF BERYLLIUM OXIDE ANION, BeO-………………….….. 43
3.1 Introduction ……………………………………………………...........................…..................................................... 44
3.2 Experimental Procedure and Spectrometer Description………………....……..….............................................. 46
3.3 Electronic Structure Calculations……………………………………………....…...................................................... 48
3.4 Experimental Results and Discussion …………...…………………….........…….................................................... 52
3.5 Conclusions…………………………………………………………………..……............................................................. 57
3.6 Chapter 3 References ………………………………………………………..…….......................................................... 59
CHAPTER 4: PHOTOELECTRON DETACHMENT SPECTROSCOPY OF BERYLLIUM SULFIDE ANION, BeS-…… 65
4.1 Introduction ……………………………………………………...........................….................................................... 66
4.2 Experimental Methods…………………………………………………....………......................................................... 68
4.3 Theoretical Calculations ……………………………………………………….…......................................................... 69
4.4 Results and Discussion …………………………………………………………..…....................................................... 73
4.4.1 SEVI Spectroscopy………………………………………..……..……................................................................... 73
4.4.2 Autodetachment Spectroscopy…………………………………..…….............................................................. 79
.4.5 Conclusions…………………………………………………………………...…….......................................................... 81
4.6 Chapter 4 References……………………………………………………….…..…......................................................... 83
CHAPTER 5: DATIVE BONDING BETWEEN CLOSED-SHELL ATOMS, THE BeF- ANION……………………......... 87
5.1 Introduction ……………………………………………………...........................….................................................... 88
5.2 Experimental and Theoretical Methods……………………………………....….…................................................. 90
5.3 Results and Discussion ……………………………………………………...….…........................................................ 92
5.4 Conclusions …………………………………………………………………...…............................................................. 97
5.5 Chapter 5 References ………………………………………………..…………..…....................................................... 98
CHAPTER 6: CHARACTERIZATION OF THE GROUND STATES OF BeC2 AND BeC2- VIA PHOTOELECTRON
VELOCITY MAP IMAGING SPECTROSCOPY……......…........................................................................................ 103
6.1 Introduction …………………………………………………….....................……....................................................... 104
6.2 Experimental Methods ……………………………………………………………......................................................... 106
6.3 Experimental Results and Discussion……………………………………………...................................................... 107
6.4 Theoretical Analysis of BeC2- and BeC2…………………………………………...................................................... 110
6.5 Conclusions………………………………………………………………………............................................................. 115
6.6 Chapter 6 References ……………………………………………………………........................................................... 116
CHAPTER 7: PRELIMINARY WORK ON VARIOUS ANIONIC SPECIES….….....…................................................ 120
7.1 Beryllium Dichalcogenides, BeX2- (X = O, S)………………….....................……................................................ 121
7.2 Beryllium Hydroxide, BeOH-……………………………………………………......................................................... 126
7.3 Beryllium Halides…………………………………………………………………........................................................... 128
7.3.1 Beryllium Monohalides, BeX- (X = Cl, Br)…………………………................................................................ 128
7.3.2 Beryllium Superhalogens BeX3- (X = F, Cl, Br)…………………...…............................................................ 131
7.4 Thorium Oxide Clusters (ThnOm-)………………………………………………........................................................ 132
7.5 Chapter 7 References ………………………………………………………….............................................................. 136
CHAPTER 8 : DISSERTATION CONCLUSIONS AND FUTURE DIRECTIONS ……................................................ 140
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