Award Date

1-1-1997

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

First Committee Member

Dennis Lindle

Number of Pages

103

Abstract

The relaxation dynamics of HCl, DCl, H{dollar}\sb2{dollar}S, and D{dollar}\sb2{dollar}S following photoexcitation in the vicinity of the Cl, and S K-shell thresholds ({dollar}\sim{dollar}2.8 keV for Cl, {dollar}\sim{dollar}2.5 keV for S) were studied by means of ion time-of-flight mass spectroscopy using monochromatic synchrotron radiation. In all cases, the onset of pre-edge core-shell photoionization precedes the formation on resonance of a significant amount of neutral hydrogen as well as post-collision-interaction effects above threshold. At the lowest resonant excitation to the 6{dollar}\sigma\sp{\*}{dollar} antibonding orbital in HCl, almost half of the excited molecules decay by emission of a neutral H atom, mostly in coincidence with a highly charged Cl{dollar}\sp{n+}{dollar} ion. The present work demonstrates that neutral-atom emission can be a significant decay channel for excited states with very-short lifetimes (1 fs). The first detailed observations of molecular fragmentation mediated by post-collision interaction between a photoelectron and an Auger electron are also presented, evidenced by the re-capture of Cl-K photoelectrons by either Cl{dollar}\sp{n+}{dollar} or H{dollar}\sp+{dollar} dissociation fragments. In addition, examination of the width of the H{dollar}\sp+{dollar} peak in HCl and H{dollar}\sb2{dollar}S spectra taken with the analyzer parallel and perpendicular to the polarization vector of the incident light indicate that the asymmetry parameter {dollar}\beta{dollar} is positive on resonance. Finally, the relaxation dynamics of CH{dollar}\sb3{dollar}Cl following core-shell excitation in the neighborhood of the chlorine K edge ({dollar}\approx{dollar}2.8 keV) were studied using multi-ion coincidence techniques. Analysis of the data provides evidence for sequential fragmentation of the molecule. In addition, for higher ionic charge states, the fragmentation mechanism was seen to change with photon energy.

Keywords

Channel; Core; Decay; Decay Channel; Deep; Deep-core-shell; Excited State; Following; Mass; Molecules; Photoexcitation; Photoexcitations; Shell; Spectroscopy

Controlled Subject

Molecular dynamics; Chemistry, Physical and theoretical

File Format

pdf

File Size

2344.96 KB

Degree Grantor

University of Nevada, Las Vegas

Language

English

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