Access Type

Open Access Dissertation

Date of Award

January 2012

Degree Type

Dissertation

Degree Name

Ph.D.

Department

Chemistry

First Advisor

Arthur G. Suits

Abstract

This dissertation focuses on the understanding the unimolecular photochemistry and dynamics

utilizing state-resolved slice imaging approach combined with the quantum-state selective

spectroscopy technique called resonance enhanced multi photon ionization (REMPI)

method. This powerful technique allows selecting the initial quantum states of the reactants

and determining the nal quantum states, energy, the orientation and alignments of

the products. In the investigations of photodissociation dynamics of acetone at 230 nm,

a bimodal distribution for the resulting CO photoproduct is identied. This observation

indicated the presence of unimolecular dissociation mechanism analogues to the roaming

dynamics reported in formaldehyde photodissociation. Moreover, another type of roaming

mechanism called \roaming-mediated isomerization" is introduced in the study of nitrobenzene

photodissociation. In this study molecules undergo roaming type isomerization

before the simple bond ssion take place. In the study of photodissociation dynamics of

tertachloroethylene (TCE) at 235 nm and 202 nm using state resolved slice imaging approach

illustrate that the dissociation take place at the ground state despite the dierence in

the excitation energies. A similar spin-orbit branching ratio of Cl/Cl* at both wavelengths

are observed due to the above dynamical behavior of the molecule. In the study of HNO3

photodissociation near 204 nm report the translational energy and angular momentum distributions

of the resulting O(1D) product. The vibrational energy distribution of the HONO

co-product, as seen through the O(1D) translational energy distribution, shows signicant vibrational energy remaining in the molecule. Analysis of the angular distributions from

both the 1F3 <-- <-- 1D2 and 1P1 <-- <-- 1D2 O probe transitions oer additional insight into the

dynamics of the dissociation of nitric acid through the S3 (2 1A0 ) excited state, helping to

resolve some outstanding questions and pointing the way to future studies. This approach

allowed us to identify new mechanisms and channels created during the photodissociation

events, calculate the branching ratios and infer the complex reactive processes in combustion,

atmospheric and interstellar chemistry.

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