PHONON-PHONON INTERACTIONS IN MOLECULAR CRYSTALS STUDIED BY ULTRASONIC METHODS

Overview & Synopsis

Internal vibrations of molecules are slightly affected by lattice effects in molecular crystals so that there are only weak interactions between internal and external phonons which give slow relaxation times in the phonon collision operator. Thus an ultrasonic relaxation may be expected in molecular crystals. In this work it is shown that this molecular relaxation may be taken into account in the framework of Akhieser's theory and a relation between sound absorption and relaxation time is given. Results obtained through acousto-optic interaction on ionic-molecular crystals are also mentioned.