Knowledge Bank

Dipheny1methylene impurity molecules in benzophenone crystals have broad ($500cm-1$ FWHH) emission and absorption spectra at temperatures greater than $20\circ K$ and at lower temperatures a sharp ($10cm-1$ FWHH) quasi-line spectrum appears. The broad bands also become structured at low temperatures, These large ``phonon sidebands” are the result of poorly resolved low frequency internal mode structure of the guest molecules mixed with the phonon sidebands due to the gest-host electron-phonon interaction. Such spectra are likely to be characteristic of many molecules with Low frequency internal vibrations. These and other spectra are discussed in terms of current theories.