“…So, in the case of exciton interaction with LO phonons cpLo may be considered to be constant only if in the frequency range h-'(-SZ + E,) 5 Y 5 K ' E , the damping depends on the frequency as ffo -I/c,f(hv -E , In the case of polaritons as well as in the case of excitons interacting with LA phonons the form of the f (v) dependence for the respective frequency regions is more complicated. Now let us compare our conclusions with experimental data obtained, e.g., in [7] as the result of measuring the reflection spectrum from the (201) face of an anthracene crystal at 4.2 K. As is seen in Fig. 1 damping in the spectral range -0 + E , 5 hv 2 E , is due only to the processes with LO phonon absorption (Q z 45 cm-' is the energy of the anthracene b-band LO phonon).…”