Date of Award

2011

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Physics

First Advisor

Chowdhury, Dr. Sazzadur (Physics)

Keywords

Physics.

Rights

CC BY-NC-ND 4.0

Abstract

A toroidal spectrometer designed to perform (γ, 2e) studies, was for the first time employed for Threshold Photoelectron Photoion Coincidence (TPEPICO) study. The angular distributions of O+(4S) ions produced from dissociative photoionization (DPI) of O c4 ( =0,1) using the TPEPICO technique, i.e. by measuring the coincidence yield between threshold photoelectrons and photoions have been investigated. The results for lifetimes, , corresponding to the vibrational levels  = 0,1, along with the value obtained for inherent anisotropic photoion angular distribution , are presented. Recently, Fernßndez and Martφn (New J Phys 11 34 (2009)), have performed an extensive ab initio study of DPI in H2, in which large oscillatory behaviour in the electron angular distribution, as a function of electron energy, has been predicted. The result of their ab anitio calculations reveal that the electron angular, , distributions oscillate between a cos2 pattern and isotropic with less than a 1 eV.change in electron energy Due to the very low cross section and the requirement for high energy resolution in the electron detection system, these measurements require sensitive instrumentation that is now available at the Canadian Light Source. For this particular H2 study, the electron angular distributions as a function of electron energy are the signature of quantum mechanical interference between, essentially, two specific doubly excited states (namely, 1Q11u+ and 1Q21u) decaying at different internuclear distances. While interference between `direct' photoionization and autoionization is well-known, the first unambiguous observation of interference between two autoionization processes, occurring on the femtosecond timescale is presented. A simple semi-classical model captures the essence of both our experimental observations and the results of full ab initio calculations. It does this through explicitly linking the electron angular distributions with the nuclear motion of the dissociating diatomic molecule.

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