The Valence Bond Approximation in Crystals — Application to an Analysis of the Ultraviolet Spectrum in Quartz

A simple band model analogous to the tight binding approximation is presented which is applicable to valence crystals. This model is applied to an analysis of the ultraviolet reflectivity data for quartz recently obtained by Loh and Philipp. It is demonstrated that the observed peaks can be understood in terms of the elementary processes of the breaking of Si‐O bonds, the promotion and demotion of atomic states, and the interaction with the crystal of electrons freed by these processes.