Phonon Structures of Optical Absorption Bands of Radicals Produced by Irradiation in Naphthalene Single Crystals

Abstract

Abstract The electronic spectra of impurities in molecular crystals are usually characterized by the presence of phonon sidebands.1–5 For a forbidden transition, the coupling with phonons may enhance the transition probability and cause phonon sidebands, which may become more intense with increasing temperature.6 For an allowed transition, sideband structures are the manifestation of the coupling between electrons and local phonons.3 If the lattice distortion around the impurity is small, the sidebands display the density of lattice phonon states. In this case the relative intensity of the sidebands to the zero-phonon line is a measure of the strength of the electronic coupling of the impurity to the surrounding molecules. If the lattice distortion is large, coupling to the local phonon modes would affect the sideband structures. Studies of electron-phonon coupling have provided important information on the impurity state in the crystal.