Basil G. Anex

Optical Properties of Highly Absorbing Crystals

Abstract Methods of obtaining polarized single crystal absorption spectra and other closely related spectral data for highly absorbing substances in the ultraviolet and visible regions are discussed. Specular reflection spectroscopy is treated in some detail, both experimental and interpretive techniques being covered, direct absorption methods are discussed, with emphasis being placed on possible sources of difficulty that can arise in crystal measurements involving high optical densities, and the importance of considering the use of other techniques to confirm the results of absorption and reflection studies is brought out. The presentation is illustrated by examples drawn from the authors current research activities.

Polarization of the Lowest‐Energy Allowed Transition of β‐Ionylidene Crotonic Acid and the Electronic Structure of the Polyenes

Polarized specular reflection spectra have been obtained for two faces of the all‐trans β‐ionylidene crotonic acid single crystal in the 700‐to‐220‐mμ region. Visual inspection of these results leads to the assignment of the absolute polarization of the lowest allowed transition, which is believed to be the first accurate absolute assignment for a polyene‐related compound. The polarization is confirmed by the integrated intensities of the absorption bands derived through a Kramers—Kronig analysis of the reflection data. The relationship between the experimental polarization and that predicted by various zero‐order theories that have been applied to the polyenes is examined and the effect of refinements in these theories on the direction and magnitude of the transition moment explored.

Polarized single crystal reflection spectra of auramine perchlorate

Abstract Polarized specular reflection spectra have been obtained for three natural faces and one cleavage face of crystalline auramine perchlorate. These spectra are interpreted in terms of known solution properties through the development of a model for the orientation of the cationic dye species in the crystal and the application of classical dispersion theory. The crystal model has been further substantiated through the study of the variation of the principal directions with wavelength on each face. Various applications of reflection spectroscopy illustrated or suggested by the present work are discussed.