Spectroscopic studies of molecules that challenge computational chemistry 公开

Abstract

The gas-phase electronic spectra of small Be-containing (Be2⁺, BeOBe⁺, BeC), Hf-containing (HfF⁺ and HfS⁺) and actinide molecules (ThF, ThF⁺, UF and UF⁺) were recorded with variety of experimental techniques. Ab initio electronic structure calculations were used to facilitate the assignment of the observed spectra.

The ground electronic states of Be2⁺ and BeOBe⁺ were probed using the PFI-ZEKE technique. The rotational symmetry selection rules were used to confirm the symmetry of the ground state as ²Σu in Be2⁺ and ²Σg⁺ in BeOBe⁺. The ionization energies were refined over previous measurements. Results from recent theoretical calculations are in good agreement with the experimental data.

Electronic spectra for BeC were recorded over the range 30500-40000 cm^-1. The vibronic structure consists of a series of bands with erratic energy spacings. Theoretical calculations indicate that the erratic vibronic structure results from strong interactions between the four lowest energy ³Π states. The predictions were sufficiently close to the observed structure to permit partial assignment of the spectra. Bands originating from the low-lying 1⁵Σ^- state were also identified, yielding a ⁵Σ^- to X³Σ^- energy interval of 2305±80 cm^-1.

The electronic spectra for HfS⁺ and HfF⁺ were recorded with PFI-ZEKE technique. Three electronic states were identified in HfS⁺ and four in HfF⁺. The ionization energies for neutral molecules, term energies and molecular constants for the ground and low-lying states of cations are reported. The results for HfF⁺ support the contention that HfF⁺ is a viable candidate for electron electric dipole moment measurements. The spacings between adjacent X¹Σ⁺ and ³Δ1levels are found to be less favorable for the proposed studies of the fine structure constant.

The low-lying states of ThF⁺ and UF⁺ were probed PFI-ZEKE photoelectron spectroscopy. Vibronic progressions belonging to four electronic states of ThF⁺ and sixteen electronic states of UF⁺ were identified. The ground state in ThF⁺ is tentatively assigned as ¹Σ⁺. The ³Δ1 state of ThF⁺, of interest for investigation of the electron electric dipole moment, is just 315.0(5) cm^-1 above the ground state. The observed patterns of low-lying electronic states of UF⁺ are consistent with ab initio calculations and ligand field theory predictions.

Table of Contents

CHAPTER I. INTRODUCTION 1

REFERENCES 6

CHAPTER II. SPECTROSCOPIC CHARACTERIZATION OF Be2⁺ X ²Σu⁺ AND THE IONIZATION ENERGY OF Be2 8

II.1 INTRODUCTION 8
II.2 EXPERIMENTAL 9
II.3 RESULTS AND ANALYSIS 12
II.4 DISCUSSION 13
REFERENCES 16

CHAPTER III. PFI-ZEKE SPECTRUM OF THE GROUND ELECTRONIC STATE OF BEOBE⁺ 25

III.1 INTRODUCTION 25
III.2 EXPERIMENTAL 26
III.3 RESULTS AND ANALYSIS 28
III.4 DISCUSSION 29
REFERENCES 31

CHAPTER IV. EXPERIMENTAL AND THEORETICAL STUDIES OF THE ELECTRONIC TRANSITIONS OF BEC 38

IV.1 INTRODUCTION 38
IV.2 THEORETICAL CALCULATIONS 40
IV.3 EXPERIMENTAL 42
IV.4 RESULTS AND ANALYSIS 44
IV.5 DISCUSSION 46
REFERENCES 51

CHAPTER V. LOW-LYING STATES OF HFS⁺ AND THE IONIZATION ENERGY OF HFS 70

V.1 INTRODUCTION 70
V.2 EXPERIMENTAL 71
V.3 AB INITIO CALCULATIONS 73
V.4 EXPERIMENTAL RESULTS 74
V.5 DISCUSSION 78
REFERENCES 80

CHAPTER VI. SPECTROSCOPIC INVESTIGATIONS OF ThF, ThF⁺ AND HfF⁺ 90

VI.1 INTRODUCTION 90
VI.2 EXPERIMENTAL METHOD 92
VI.3 NOTATION 94
VI.4 RESULTS 94

VI.4.1 SPECTROSCOPY OF HFF⁺ 94
VI.4.2 REMPI AND LIF SPECTRA OF NEUTRAL THF 96
VI.4.3 MEASUREMENT OF THE THF IONIZATION ENERGY AND THE SPECTROSCOPY OF THF⁺ 98

VI.5 ELECTRONIC STRUCTURE CALCULATIONS OF THF AND THF⁺ 103
VI.6 DISCUSSION 105

VI.6.1 HFF⁺ SPECTRAL ASSIGNMENT 105
VI.6.2 THF AND THF⁺ SPECTRAL ASSIGNMENT 106
VI.6.3 IONIZATION AND BOND DISSOCIATION ENERGIES 108

REFERENCES 109

CHAPTER VII. SPECTROSCOPIC AND THEORETICAL INVESTIGATIONS OF UF AND UF⁺ 131

VII.1 INTRODUCTION 131
VII.2 EXPERIMENTAL 133
VII.3 NOTATION 135
VII.4 CALCULATIONS 135
VII.5 RESULTS 137
VII.6 ANALYSIS AND DISCUSSION 139

VII.6.1 UF 139
VII.6.2 UF⁺ 142

VII.7 CONCLUSIONS 147
REFERENCES 148

APPENDIX. SUPPLEMENTARY MATERIAL ON BeC CALCULATIONS 167

About this Dissertation

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School	Laney Graduate School
Department	Chemistry
Degree	PhD
Submission	Dissertation
Language	English
Research Field	Chemistry, Physical
关键词	Gas-phase spectroscopy Pulsed field ionization zero electron kinetic energy (PFI-ZEKE) Spectroscopy of actinides Spectroscopy of cations Quantum chemistry Spectroscopy of beryllium compounds
Committee Chair / Thesis Advisor	Heaven, Michael, Emory University
Committee Members	Lian, Tim, Emory University Bowman, Joel M, Emory University

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