Investigations of intramolecular dynamics by picosecond time-resolved spectroscopy
Smith, Philip Gordon
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https://hdl.handle.net/2142/22419
Description
Title
Investigations of intramolecular dynamics by picosecond time-resolved spectroscopy
Author(s)
Smith, Philip Gordon
Issue Date
1991
Doctoral Committee Chair(s)
McDonald, J. Douglas
Department of Study
Chemistry
Discipline
Chemistry
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Chemistry, Physical
Language
eng
Abstract
Intramolecular vibrational energy redistribution (IVR) is studied by picosecond time resolved fluorescence depletion (TRFD), a technique which directly measures the ultrafast relaxation processes of the initially prepared vibronic level. Fluorescence depletion decays and dispersed fluorescence spectra of 19 vibronic features in the isolated gas phase molecule p-cyclohexylaniline are presented. The excellent match of the laser system's tuning curve with the fluorescence excitation spectrum of this molecule allows the convenient study of vibronic levels as high as 2364 cm$\sp{-1}$. This represents the widest energy range in a time domain IVR study to date. The decays show a progression of dynamic behavior including stationary behavior at low state densities, quantum beating at intermediate densities, and fast decays at high state densities. A companion technique, called time resolved stimulated emission pumping (TRSEP), is used to obtain decays for three of the 19 vibronic levels in p-cyclohexylaniline. These TRSEP decays allow one to quantitatively measure the ratio of fast to slow fluorescence intensities in order to obtain accurate values for the number of coupled states. This data inspired us to take a closer look at the time decays which eventually led to the understanding of why the medium energy levels exhibit temporal behavior with fast initial decays and small damped quantum beats when large undamped quantum beats are expected. This thesis demonstrates that the rotational state interactions are the cause for this interesting behavior.
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