The temperature dependence of the electron nuclear double resonance spectra of FH(CN-) centers was investigated between 10 and 220K. At 10K, only one CN- orientation (with respect to the F center electron) was present; in which the N was thought to be nearer to the F-electron than the C. After surmounting a very small thermal activation energy of 0.0029eV, the opposite orientation was occupied. The superhyperfine interactions of the first shell K nuclei which were nearest to CN-, and of the 13C interaction of the CN- molecule, were markedly temperature dependent between 10 and 60K and obeyed an exponential law with a thermal activation energy of 0.0042eV. It was assumed that a soft local mode which involved the 2 nearest K nuclei and CN- led to the strong temperature dependence.

T.Pawlik, R.Bungenstock, J.M.Spaeth, F.Lüty: Radiation Effects and Defects in Solids, 1995, 134, 465-70