## LSU Historical Dissertations and Theses

1998

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Chemistry

Erwin D. Poliakoff

#### Abstract

Using synchrotron radiation as an excitation source, dispersed fluorescence measurements of two different molecular systems are presented in this dissertation with the intention to study the two fundamental aspects of shape resonances-complexity and completeness. $\rm C\sb6F\sb6$ is a relative large and complex molecule in the sense that nonradiative transitions can take place unimolecularly in the free species. The elucidation of the ionization dynamics of this molecule helps to bridge the gap from simple molecules to matter in condensed phases. In the $\rm 2a\sb{2u}\sp{-1}$ photoionization study of $\rm C\sb6F\sb6,$ the non-Franck-Condon behavior of the vibrational distributions at around 20 eV indicates the existence of shape resonances in this energy range. This is the first time a shape resonance of such a complex molecule is characterized with vibrational resolution detail over such a broad energy range. While the study of $\rm C\sb6F\sb6$ is to disentangle the complexity aspect of shape resonance, the investigation of CO is an attempt to carry the shape resonant study to its completeness. The original goal of the $4\sigma\sp{-1}$ photoionization study of CO was to investigate the vibrational-rotational-electronic (V-R-E) coupling. To be specific, we intended to study the shape resonant effects on the rotational population distributions for alternative vibrational levels. While the $4\sigma\to k\sigma$ shape resonance influences do not seem to be very significant, the results brought to attention another issue--continuum-continuum channel coupling. The study shows that the R-dependent aspects of shape-resonance-induced continuum coupling affects rotational population distributions for alternative vibrational states differently. In modern scientific researches, the development of instruments plays a critical role. The trend today is for computers to serve as the engine for instrumentation-virtual instruments. By walking through the development processes of a real-time instrument control and data acquisition system, the hardware setup as well as the software design and implementation, this dissertation intends to illustrate the advantage of virtual instruments over traditional instruments.

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