Dipolar Coupling and Molecular Vibration in Crystals. I. General Theory

Abstract

Coupling of the transition dipoles associated with infrared-active vibrations produces one source of frequency shift and splitting of transverse and lingitudinal modes in solids. The intrinsic part of the dipole is distinguished from the induced part, the latter being related to the electronic polarizabilities of the molecular or atomic units in the structure. Although approximate treatments neglecting the induced part of the dipole have been given previously and, also, certain estimates of the effective field (related to the induced dipole) have appeared earlier in the literature, we here take both effects fully into account for a number of noncubic crystal structures.