Stress-induced dichroism of the vibrational lines and phonon sidebands of SH- centres in CsBr

Paraelastic alignment of SH- centres in CsBr leads to a stress-induced dichroism of the infrared absorption lines and their phonon sidebands. The principal values of the elastic dipole tensor are determined from quantitative infrared measurements under uniaxial stress. The centres turn out to be <100> oriented and have a disk-shaped elastic dipole tensor. The stress-alignment is used to determine the polarization of the phonon sidebands with respect to the molecular axis. Those irreducible representations, by which phonons and localized modes mainly couple to the intramolecular vibration, are derived with the help of group-theoretical considerations. Selection rules for the appearance of particular phonons in the sidebands are discussed. (author)