Rotational and vibronic effects in molecular electronic spectra

Abstract

This thesis falls into three distinctly different parts, to each of which a chapter is devoted. The three topics examined aim for a further understanding of the electronic spectra of polyatomic molecules, particularly aromatic molecules. The first chapter is mainly concerned with the rotational fine structure accompanying vibronic bands in a newly synthesized isomer of benzofuran, and contains a detailed interpretation of such a band within the rigid rotor approximation. Chapter 2 represents the bulk of the experimental portion of the thesis, and, apart from two unrelated sorties, is an investigation of the electronic spectra of substituted azulenes. The goal of that study was a better understanding of the complex, solvent-sensitive vibronic effects in the second transition of azulene. Solution, vapour and mixed crystal spectra of four substituted azulenes were recorded to assist in the investigation. The two other investigations described in Chapter 2 concern purine and dicyanoacetylene. Chapter 3 investigates a simple, yet rather successful, method for the quantitative prediction of the extent to which symmetric and nontotally symmetric vibrations may couple one electronic state to higher states of the appropriate symmetry. The method is tested by application to a variety of molecules. This chapter has some links with Chapter 2, and in particular the gross effects in the spectrum of azulene, already referred to, are largely accounted for by the calculations. Because of the disparate natures of the three studies, it will be convenient to offer separate discussions of each topic in the appropriate chapter. All the frequencies recorded in this thesis are corrected to vacuum. Axes conventions throughout, are those recommended by Mulliken.