Theory Of Electronic Spectra Research Articles

Band shape analysis of electronic spectra of polar dye solutions

A semiclassical theory of electronic spectra of polar dye solutions is presented and analytical expressions of the spectra are given. A quasi-molecular approach is applied and the quasi-molecule model of the spectra previously published is reanalyzed. It is assumed that a large-amplitude motion plays a key role in the broadening of the spectra of polar dye solutions. An energy-level diagram of a quasi-molecule, considered as a dye molecule with its nearest neighborhood, is presented. In addition, the energy of reorientation in going from a Franck-Condon to an equilibrated state is determined. The orientation energy is equal to that part of the excitation energy given by the difference of the excited Franck-Condon state of a quasi-molecule from that of its equilibrated excited state. It is shown that after excitation, not only is excess vibrational, but also part of the electrostatic interaction energy is transferred to the surroundings. This energy may be obtained directly from absorption and fluorescence spectra of polar dye solutions. Experimental verification is performed on several coumarin solutions. The mean value for the reorientation energy in this case is found to be 645 cm-1.

A Semi-Empirical Theory of the Electronic Spectra and Electronic Structure of Complex Unsaturated Molecules. II

The theory of electronic spectra and electronic structure, the elucidation of which was begun in the first paper of this series, is further developed and applied to ethylene, butadiene, benzene, pyridine, pyrimidine, pyrazine, and s-triazine. A realistic and consistent LCAO-MO π-electron theory should allow the σ-electrons to adjust themselves to the instantaneous positions of the mobile π-electrons. This is accomplished in the theory by assignment of empirical values to the Coulomb electronic repulsion integrals and Coulomb penetration integrals which enter the formulas, these values being obtained in a prescribed way from valence state ionization potentials and electron affinities of atoms. Use of the empirical values in the molecular orbital theory reduces the magnitude of computed singlet-triplet splittings and the effects of configuration interaction without complicating the mathematics. From the valence-bond point of view, ionic structures may be said to be enhanced. The applications to hydrocarbons and heteromolecules which are considered show that the theory can correlate known π-electron spectral wavelengths and intensities very successfully, which, together with the simple structure of the theory, signals that manifold applications of the theory are in order elsewhere.