Vibrational coupling of F centers to the stretch mode of neighboring CN--molecules in KCl

We determined the electronic-vibrational (E-V) coupling within an F center- CN- pair by detecting the vibrational sideband structure in transient absor ption measurements. The obtained Huang-Rhys factor S-CN = 0.005 and the cor responding shift in CN- equilibrium distance Delta Q(0) = 0.005 Angstrom ar e compared with previously measured ones in CsCl and CsBr. Based on these r esults the E-V transfer rates expected in a horizontal tunneling model are estimated and good agreement with experimental data is obtained.