Temperature Dependence of Hyperfine Structure Tensors of Diatomic Halogen Centres in Alkali Halide Crystals

The ESR‐spectra of diatomic halogen centres of the type X and XY− in alkali halides show temperature dependent line positions due to changes of the hfs‐constants. The temperature dependent part of the hfs‐tensors is determined from an analysis of these spectra. The mechanisms leading to the temperature dependence are discussed: crystal lattice vibrations and resonant vibrations of the molecule modulate the crystal field. This lowers the electron density at the nuclei of the molecule as the vibrational amplitude increases. The frequencies of the molecular vibrations are determined from the experimental data. The effect of the lattice on the force constants is discussed with reference to the comparison of these values with those for the corresponding free molecules.