RELAXATION OF THE CN- STRETCHING VIBRATION IN SILVER-HALIDES - THE ROLE OF ACCEPTING MODES

The vibrational relaxation of CN- in AgCl and AgBr is found to be 1000 times faster than in the potassium, rubidium, and cesium halides, mea sured previously. We demonstrate that high-frequency local modes are t he source of this difference, which also explains the short times foun d earlier for CN- in the sodium halides. An energy gap law fits all of the data, with the highest frequency bulk or localized phonon as the accepting mode. Extrapolating this law down to a single accepting mode , we obtain a subnanosecond lifetime, in agreement with previous measu rements of CN- in aqueous solution.