INVESTIGATION OF THE DYNAMICAL BEHAVIOR OF THE F-H(CN-) CENTER IN KCLWITH TEMPERATURE-DEPENDENT ENDOR SPECTROSCOPY

The temperature dependence of the electron nuclear double resonance (E NDOR) spectra of F-H(CN-) centres in KCl was investigated in the tempe rature range between 10-220 K. At the lowest temperature of 10 K only one CN- orientation with respect to the F centre electron is present, in which the nitrogen is thought to be nearer to the F-electron than t he carbon. With the very small thermal activation energy of 2.9 meV th e opposite orientation is occupied. The superhyperfine interactions of those first shell K nuclei nearest to CN- and of the C-13 interaction of the CN- molecule are strongly temperature dependent between 10 and 60 K, following an exponential law with a thermal activation energy o f 4.2 meV. It is assumed that a soft local mode involving those two ne arest K nuclei and the CN- is causing the strong temperature dependenc e. The shf interactions of N-14 nuclei have not been seen, probably be cause of the dynamical effects.