| Summary: | This thesis attempts to answer the question of how electrons interact with a molecular framework prior to and during emission through photoionization. These studies interrogate several behaviors of allowed and forbidden photoelectron transitions such as shape resonances, non-resonant intrachannel vibronic coupling as a result of Cooper minima, and chemically-induced nonresonant coupling, all of which provide new insights into correlations between the electronic and molecular degrees of freedom. Research presented in this thesis utilizes high-resolution photoelectron spectroscopy, and undulator-based synchrotron radiation at the Advanced Light Source, a synchrotron radiation source in Berkeley, California. Data are collected from near threshold to several hundred electron volts (eV) above the ionization potential. The approach is to examine how an ejected continuum photoelectron scatters and subsequently interacts with the molecular framework prior to emission. A new mechanism for mode specific vibronic coupling was also uncovered using the case of ICN ionization. As opposed to a Cooper minimum, or shape resonance produced from a bond length dependence for the continuum photoelectron as seen with N2 and CO, the new mechanism results from a charge-transfer process in the initial electronic state. For both cases, the results express how a strong dependence of bond length can invalidate fundamental spectroscopic approximations. In an attempt to probe larger asymmetric systems for nonresonant behavior, gas phase nucleobases were examined for vibrational structure.
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