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Femtosecond time-resolved spectroscopy of gas-phase anions: electron solvation and chromophore dynamics

Citation

Lee, I-Ren (2011) Femtosecond time-resolved spectroscopy of gas-phase anions: electron solvation and chromophore dynamics. Dissertation (Ph.D.), California Institute of Technology. http://resolver.caltech.edu/CaltechTHESIS:12082010-143906786

Abstract

This thesis presents the studies of ultrafast dynamics of negatively charged molecules and clusters in the gas phase using femtosecond photoelectron spectroscopy. The core motifs of two distinct complex systems — solvated electrons and protein chromophores — were studied in the gas phase. For the solvated electron systems — hydrated electrons and ammoniated electrons — were studied in finite-sized clusters in the gas phase. Interestingly, the results show a significant difference. In the hydrated electron, ground-state vibrational cooling is evident by the transient photoelectron spectra, while, in the ammoniated electron, a coherent motion with a 500-fs relaxation is observed. The difference is attributed to the cage rigidity, which results in different solvent motions for the electron’s interaction with water (libration) or ammonia (phonon-like). The photocycle of the photoactive yellow protein (PYP) has been studied extensively, but the dynamics of the isolated chromophore responsible for the transduction of phototacticity is less known. The anionic chromophore model molecule was investigated in the gas phase using femtosecond photoelectron spectroscopy and the results indicate that the protein function is in directing efficient conversion to the cis-structure and in impeding radical formation within the protein. Finally, a classic system of conformational twisting, stilbene, was studied in its anionic radical state. Ultrafast conversions from both trans- and cis- isomers are accompanied with coherent oscillation, in contrast to observations in the solution phase, and this suggests that a major solvent retardation take place. Dynamic studies of the photochemistry of gas-phase anions are very scarce due to the experimental difficulties. However, our results successfully resolve the photophysics and photochemistry of the isolated species and, thereby, elucidate the effect of solution.

Item Type:Thesis (Dissertation (Ph.D.))
Subject Keywords:Femtochemistry, Photoelectron, Gas-phase, Anion, Clusters, Photoactive Yellow Protein, Photoisomerization
Degree Grantor:California Institute of Technology
Division:Chemistry and Chemical Engineering
Major Option:Chemistry
Thesis Availability:Public (worldwide access)
Research Advisor(s):
  • Zewail, Ahmed H.
Thesis Committee:
  • McKoy, Basil Vincent (chair)
  • Zewail, Ahmed H.
  • Dervan, Peter B.
  • Okumura, Mitchio
Defense Date:22 November 2010
Author Email:irlee (AT) caltech.edu
Record Number:CaltechTHESIS:12082010-143906786
Persistent URL:http://resolver.caltech.edu/CaltechTHESIS:12082010-143906786
Default Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:6199
Collection:CaltechTHESIS
Deposited By: I-Ren Lee
Deposited On:23 Dec 2010 19:29
Last Modified:26 Dec 2012 04:32

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