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Date of Award

Summer 8-15-2016

Author's School

Graduate School of Arts and Sciences

Author's Department

Chemistry

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

In this work, ion time-of-flight velocity-map imaging (TOF-VMI) is combined with laser-induced fluorescence (LIF) to accurately measure the ground-state binding energies of the T-shaped and linear Ar∙∙∙I2(X,νʺ=0) complexes. LIF spectra were used to identify the transitions used to preferentially excite either the T-shaped or linear Ar∙∙∙I2(B,νʹ) conformer. The kinetic energy distributions of I2(B,ν=νʹ−3) fragments formed with low kinetic energies via dissociation of the initially prepared Ar∙∙∙I2(B,νʹ) intermolecular levels were imaged to measure the binding energies of the T-shaped and linear conformers. The linear conformer is energetically preferred with a binding energy of 250.2(2.7) cm−1, over the T-shaped conformer, which has a binding energy of 240.5(3.6) cm−1.

Most of the experimental results in this dissertation characterize the dynamics of the Ar + I2(B,νʹ) potential energy surface (PES). The intermolecular vibrational levels bound in the Ar + I2(B,νʹ=20-23) PESs are recorded using two-color action spectroscopy. Transitions of both the T-shaped and linear ground-state conformers are identified. There is a high density of intermolecular features observed in the spectra, due in part to the depth of the Ar + I2(B,νʹ) excited-state PESs and the resultant overlap of features bound within the different PES. Comparisons of the spectral shifts of the features from different I2 B−X. νʹ−0 bands are used to identify the levels bound within each of the Ar + I2(B,νʹ) PESs. At least 17 bound intermolecular levels are identified. The lowest levels correspond to the Ar atom localized in the T-shaped well, and the highest levels correspond to the Ar atom delocalized about the I2 molecule.

Identification of these levels and their associated geometries are used to characterize the nature of intramolecular vibrational redistribution (IVR) upon excitation of the complex. Ion TOF-VMI is used to characterize the dissociation dynamics of T-shaped Ar∙∙∙I2(B,νʹ). The angular anisotropy of the I2(B,ν<νʹ) fragments are measured to probe the energetics and geometries of the Ar∙∙∙I2(B,νʹ) intermolecular vibrational levels sampled during dissociation. The anisotropy is compared with the probability distributions of the levels accessible in order to identify the Ar∙∙∙I2(B,ν<νʹ) levels that are likely involved in the IVR mechanism. For certain νʹ, the I2 angular distributions indicate IVR dominates over direct vibrational predissociation (VP).

IVR is also involved in electronic predissociation (EP). VMI is used to detect atomic I(2P3/2) fragments formed from EP of the prepared T-shaped Ar∙∙∙I2(B,νʹ) level. The angular distributions of the I(2P3/2) fragments confirm that EP occurs via nonadiabatic interactions with dissociative electronic states. The kinetic energy distributions of the departing fragments have a bimodal distribution, which indicates the EP occurs from an asymmetric geometry, not the rigid T-shaped geometry of the initially prepared Ar∙∙∙I2(B,νʹ) level. IVR occurs prior to interaction with the repulsive electronic state and the changes in geometry associated with IVR support theoretical predictions that the a′(0g+) dissociative state is the one that most contributes to EP. Comparison of the I(2P3/2) yield from EP and the I2(B,ν<ν′) yield from VP reveals that the two processes are in competition with each other.

The Ar + I2(E,ν†) interactions were also investigated. Laser-induced fluorescence spectra identifying a large number of Ar···I2(E,ν†=0-3) intermolecular vibrational levels were recorded using metastable Ar···I2(B,ν=23) levels as intermediates in a two-color, two-photon excitation scheme. A binding energy of 410.3(3.6) cm–1 is established for the T-shaped complex in the Ar + I2(E,ν†=0) potential energy surface.

Language

English (en)

Chair and Committee

Richard A. Loomis

Committee Members

Richard Mabbs, Jacob Schaefer, Bryce Sadtler, Erik Henriksen

Comments

Permanent URL: https://doi.org/doi:10.7936/K7GF0RX8

Available for download on Saturday, August 15, 2116

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