Chemical Reaction Dynamics at the Statistical Ensemble and Molecular Frame Limits
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Authors
Clarkin, Owen
Date
2012-09-12
Type
thesis
Language
eng
Keyword
Femtosecond Laser , Coincidence Imaging Spectroscopy , Scattered Light Background Reduction , Dendritic Cupric Oxide , Time Resolved Photoelectron Spectroscopy , Effect of Air Pressure on Laser Performance , Effect of Weather on Laser Performance , Transition state theory , Imaging Valence Electronic Dynamics , Non-Adiabatic Alignment , Time Resolved Photoelectron Angular Distributions , Excited States , Conical Intersections , Molecular Frame , Potential Energy Surfaces , Time Dependent Density Functional Theory , Chemical Reaction Dynamics , Flexible Transition State Theory , Carbon Disulfide
Alternative Title
Abstract
In this work, experimental and theoretical approaches are applied to the study of chemical reaction
dynamics. In Chapter 2, two applications of transition state theory are presented: (1) Application of
microcanonical transition state theory to determine the rate constant of dissociation of C2F3I
after π∗ ← π excitation. It was found that this reaction has a very fast rate constant
and thus
is a promising system for testing the statistical assumption of molecular reaction dynamics. (2) A general
rate constant expression for the reaction of atoms and molecules at surfaces was derived within the statistical
framework of flexible transition state theory.
In Chapter 4, a computationally efficient TDDFT approach was found to
produce useful potential energy surface landscapes for application to non-adiabatic predissociative dynamics
of the molecule CS2 after excitation from the ground state to the singlet C-state. In Chapter 5, ultrafast
experimental results of excitation of CS2 to the predissociative neutral singlet C-state is presented. The
bandwidth of the excitation laser was carefully tuned to span a two-component scattering resonance with each
component differently evolving electronically with respect to excited state character during the quasi-bound
oscillation. Scalar time-resolved photoelectron spectra (TRPES) and vector time-resolved photoelectron
angular distribution (TRPAD) observables were recorded during the predissociation. The TRPES yield of
photoelectrons was found to oscillate with a quantum beat pattern for the photoelectrons corresponding to
ionization to the vibrationless cation ground state; this beat pattern was obscured for photoelectron energies
corresponding to ionization from the vibrationally excited CS2 cation. The TRPAD data was recorded for
two general molecular ensemble cases: with and without a pre-excitation alignment laser pulse. It was found
that in the case of ensemble alignment (Chapter 6), the “molecular frame” TRPAD (i.e. TRMFPAD) was
able to image the purely valence electronic dynamics of the evolving CS2 C-state. The unaligned ensemble
TRPAD observable suffers from excessive orientational averaging and was unable to observe the quantum
beat.
Engineering efforts were also undertaken to eliminate scattered light background signal (Chapter 7,
Appendix A) and improve laser stability as a function of ambient pressure (Appendix B) for TRMFPAD
experiments.
Description
Thesis (Ph.D, Chemistry) -- Queen's University, 2012-09-11 22:18:20.89
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