Electronic spectroscopy, kinetics and photodissociation dynamics of gas phase cations

by Stringer, Kay Lesley

Abstract (Summary)
A thorough understanding of the chemical and physical properties of small molecules involves spectroscopy, thermodynamics, kinetics and dynamics of the system. This thesis highlights the use of photochemistry to measure these properties for Au+ (C2 H4 ), Pt+ (C2 H4 ) and ethylbenzene cation as well as for deposition of zeolite films. Chapter 1 highlights the principles behind photodissociation and the information that can be obtained from spectroscopy. Also discussed is what the appearance of the photodissociation spectrum and time-of-flight profile implies about the molecular dynamics and kinetics. Chapter 2 examines gas-phase photodissociation of the classic � complexes Au+ (C2 H4 ) and Pt+ (C 2 H4 ). Spectroscopic onsets provide upper limits to the metal-ligand bond strengths of 344 kJmol-1 and 230 kJmol-1 for Au+ (C2 H4 ) and Pt + (C2 H4 ) respectively. The spectrum of Au + (C2 H4 ) features an extended progression in the metal-ligand stretch with a frequency of 176 cm-1 that drops to 160 cm-1 in Au+ (C 2 D4 ). Hybrid density functional theory (DFT) calculations and TD-DFT calculations are used to explore the structures, bonding and electronic spectroscopy of the two complexes. The photodissociation pathways and kinetics of the ethylbenzene radical cation are investigated in Chapter 3. The energy dependence of the various pathways are investigated. The most abundant dissociation channel is C 7 H7+ + CH3 at all wavelengths, but C6 H4+ + C2 H6 and C6 H6+ + C2 H4 are also important in the near-UV. The C6 H4+ + C2 H6 pathway is especially interesting as it exhibits a significant peak broadening with â¼0.6 eV kinetic energy release. Later studies using vibrationally cold ions examined the dissociation rate, k(E), at various photon energies. Simulations of the time of flight profile show that the k(E) increases from 0.97 �-- 106 s-1 at 2.38 eV to 2.6 �-- 106 s -1 at 2.67 eV internal energy. An alternate application of molecule-light interaction to surface science is explored in Chapter 4. Here, the technique of pulsed laser deposition has been employed in efforts to improve thin film growth for ETS-4 molecular sieves. Characterization using X-Ray Diffraction and Transmission Electron Microscopy confirm that the zeolite structure is unaltered during the deposition process. Recommendations for further studies are discussed in Chapter 5.
Bibliographical Information:


School:University of Massachusetts Amherst

School Location:USA - Massachusetts

Source Type:Master's Thesis



Date of Publication:01/01/2004

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