Theoretical Simulation of K-Edge X-Ray Absorption Spectra for Methane and Its Fluorinated Derivatives Open Access

Abstract

X-ray absorption spectroscopy (XAS) has been widely studied as an element-specific technique to determine the electronic properties of molecules. Experiments have been conducted on methane and its fluorinated derivatives, a family of chemicals with significant impact in chemistry and environmental science, to investigate their electronic properties. With the development of advanced computational techniques, the electronic nature of the core excitations involved in XAS can be better understood. In this experiment, we employ both the time-dependent density functional theory (TDDFT), a single-reference density-based method, and the multiconfigurational self-consistent field (MCSCF) with the generalized active space self-consistent field method (GASSCF) as a reference to simulate the carbon and fluorine K-edge X-ray near edge spectra (XANES) of CHnF4-n (n=0-4). We compare the two methods with experimental data to investigate the excitation contribution to the spectral features. We also analyze the spectra to explore how electronic properties can be reflected in the spectra.

Table of Contents

1.    Introduction                                                                                                                       

1.1 X-ray Spectroscopy Theory                                   1

1.2 Methane and Its Fluorinated Derivatives                                                                          

1.2.1 Overview                                                              2

1.2.2 Environmental Impacts                                      3

1.3 Purpose                                                                                 4

2. Computational Methods                                                                                                           

2.1 Geometry Optimization and Energy Determination   5

2.2 Time-dependent Density Functional Theory                                                                    

2.2.1 Background                                                                       6

2.2.2 Computation Setup                                                         7

2.3 Multiconfigurational Self-Consistent Field Method

2.3.1 Background                                                                       7

2.3.2 Computation Setup                                                         9

3. Results

3.1 Geometry and Energetics                                                  10

3.2 XANES Spectral Features                                                   10

3.3 Excitation Contribution                                           11

4. Discussion                                                                   12

5. Code Availability                                                                      13

6. Reference                                                                                    14

7. Tables/Figures/Schemes                                                          17

About this Honors Thesis

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School	Emory College
Department	Chemistry
Degree	B.S.
Submission	Honors Thesis
Language	English
Research Field	Chemistry, Physical
Keyword	GASSCF Multireference Core Excitation XANES TDDFT X-ray spectroscopy
Committee Chair / Thesis Advisor	Francesco A. Evangelista, Emory University
Committee Members	Michael Heaven, Emory University Katherine M. Davis, Emory University

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