FREQUENCY DISPERSION EFFECTS IN MULTIPHONON TRANSITIONS.

It is shown that the phonons emitted in a multiphonon transition obey a simple distribution law with respect to the phonon energy. It implies that the relative roles of phonons of different frequencies change systematically with the transition energy and affect accordingly the multiphonon transition probability. The prevalent use of single-frequency models, which completely obliterates such effects, can thus be seriously inappropriate. Such inadequacy of single-frequency models is illustrated by comparing results calculated from multi-frequency models and corresponding single-frequency models.