LSU Historical Dissertations and Theses

1996

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Chemistry

Erwin D. Poliakoff

Abstract

Using the method of detecting dispersed fluorescence from electronically excited photoions, measurements of their vibrational and rotational distributions over a 200 eV photon energy range are presented. The vibrational distributions following 2$\rm\sigma\sb{u}\sp{-1}$ photoionization of N$\sb2$ show a non-Franck-Condon behavior over a very broad energy range of nearly 100 eV. Comparison of these new results with detailed theoretical calculations of Wang & McKoy allow the interpretation of this Franck-Condon breakdown as arising from a dependence of Cooper minima on molecular bond length. The results highlight the molecular character of photoionization dynamics, even deep in the ionization continuum. For a detailed investigation of the R-dependence of the Cooper minima, rotational state resolved measurements into alternative vibrational channels are determined over the same photo-excitation energy range as was carried out for the vibrationally resolved measurements. By simultaneously determining the vibrational and rotational energy deposition into the photoion, we investigate vibrational-rotational-electronic (V-R-E) coupling over a broad range of electron energy. These N$\sb2$ results help better characterize the underlying dynamics of photoionization and the role of molecular Cooper minima. Vibrational distribution measurements are presented for the iso-electronic species CO over a similar energy range. The effectiveness of dispersed fluorescence measurements as a survey tool for picking out near-edge structure is demonstrated in the results of K-shell photoionization measurements of N$\sb2$.

9780591133394

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