## LSU Historical Dissertations and Theses

1996

Dissertation

#### Degree Name

Doctor of Philosophy (PhD)

#### Department

Chemistry

Erwin D. Poliakoff

#### Abstract

Measurements of dispersed fluorescence from electronically excited photoions are used to study fundamental molecular scattering phenomena. Our experimental advances make it possible to obtain vibrationally resolved data that offer qualitative insights into photoionization dynamics in polyatomics. In particular, vibrationally resolved data are measured to probe the correlation of electronic and nuclear degrees of freedom via studying the vibrational distributions of photoions and ionic fragments. Vibrational branching ratios are mapped out over an extremely broad energy range ($\rm3\leq E\sb{k}\leq 200 eV$) for N$\sb2$O (7$\sigma\sp{-1}$) ionization channel. The origin of the non-Franck-Condon behavior is tentatively interpreted as shape resonances and Cooper minima. The alternative vibrational mode, the bending degree of freedom, is studied for two isoelectronic molecules N$\sb2$O and CO$\sb2$. The results reveal very interesting information about the trapping site of shape resonant photoionization in a polyatomic molecule: bending motion may change the width of the "box" which traps the photoelectron. The multichannel aspect of shape resonances reflected in continuum channel coupling is investigated for CO$\sb2$ ($\rm3\sigma\sb{u}\sp{-1}$) channel. Current results are in very good agreements with calculations by Lucchese and McKoy. The dispersed fluorescence spectra of the fragments $\rm N\sb2\sp+(B\sp2\Sigma\sb\mu\sp+,\ v\sp+ = 0)$ following dissociative photoionization of N$\sb2$O are measured in $\rm20\leq h\nu\sb{exc}\leq150$ eV. Characteristic features observed in the excitation spectrum of $\rm N\sb2\sp+(B\sp2\Sigma\sb\mu\sp+)$ are discussed with a focus on (pre)dissociation of (1) singly ionized parent states; (2) multielectron excitation states commonly observed in the inner-valence regions; (3) doubly ionized parent states. The multielectron excitation states and doubly ionized parent states are responsible for most of the dissociative ionization that occurs in N$\sb2$O above $\sim$22 eV. Strongly dissociative nature of doubly ionized states correlating with the single-hole 4$\sigma$ shape resonance in inner-valence region is probably responsible for the broad enhancement observed in the CIS curve. The dispersed fluorescence provides information about the internal energy distributions of the fragments and, as a consequence, leads to insights into the dissociation dynamics.

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