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Photodissociation Dynamics and Photoelectron Imaging Spectroscopy of Anions and Anion Clusters

TitlePhotodissociation Dynamics and Photoelectron Imaging Spectroscopy of Anions and Anion Clusters
Publication TypeThesis
Year of Publication2004
AuthorsSanford, TJ
Abstract

The objective of this dissertation is to study the broad topic of solvation by investigating the effects of a solvent environment on small anion solutes in gas-phase clusters. The dihalide solute chromophore, IBr-, is solvated by a controllable amount of CO2 molecules and photodissociated with tunable laser radiation. The subsequent solvent-dependent dynamics are monitored by detection of ionic photofragments. The second solute-solvent system involves Cu- solvated by H2O molecules with solvent effects on the atomic anion solute studied by photoelectron imaging spectroscopy to monitor solvent-dependent changes in the photoelectron spectrum of the solute.

The first part of the dissertation involves a detailed discussion of the two experimental methods with the previously described cluster ion source and tandem time-of-flight mass spectrometer briefly discussed focusing on modifications made to the existing system for the study of IBr-(CO2)n cluster ions. The remaining portion of the section describes in detail the design and operation of a new velocity-map imaging photoelectron spectrometer.

The second part of the dissertation describes the results of the photodissociation of mass-selected IBr-(CO2)n cluster ions. In one-color experiments, the clusters are excited to two electronic states of the solute anion and the product distributions measured as a function of cluster size. These results are compared to previous studies on ICl-(CO2)n and I2-(CO2)n clusters. The dynamics after photoexcitation are shown to be highly dependent on the number of solvent molecules attached and on the identity of solute anion. The solvent is shown to drive such processes as charge-transfer, spin-orbit relaxation, and vibrational relaxation. A femtosecond time-resolved experiment is carried out on IBr-(CO2)8 to determine timescales for these events.

The final part of the dissertation investigates the photoelectron imaging spectroscopy of Cu-(H2O)n (n = 1,2) clusters to determine the effect of solvation on an atomic anion solute. The technique of velocity-map imaging is used to produce high resolution images from which the photoelectron energy spectra and photoelectron angular distributions are obtained. Solvation shifts the Cu- features to higher binding energies along with broadening the spectral features. There are also features present assigned to the water solvent molecules that are confirmed by deuteration experiments.