Implications of Ligand Field Theory for Substitutional and Interstitial H Atoms and H− Ions in the Alkali Halides and Alkaline Earth Fluorides

It is shown that the model developed for the U2 centre in the alkali halides [1] is qualitatively successful in accounting for the magnetic properties of substitutional and interstitial hydrogen centres in the alkaline earth fluorides. An interconnection between the present theory and that required in the theory of the hyperfine interaction of F centres in these compounds is also pointed out, as well as a suggestion for utilizing the Löwdin orthogonalization technique as a means of quantitatively estimating covalency effects for the various shells of ligands next to a hydrogen impurity. Following a discussion of the properties expected for U3 centres in the alkali halides, certain possible anomalies in the recent assignment [2] of ESR data to such a centre are pointed out. Finally the optical absorption spectra of U centres are investigated and attention is drawn to the fact that a combination of odd parity vibrations, odd harmonic crystal field components, and covalency effects can make allowed s → s and s → d one‐electron dipole transitions in addition to the usual s→p transitions. The resulting implications are briefly discussed.