ENDOR Investigation of H 1 0 (Li) Centres in KCl

In KCl doped with Li + recently a new paramagnetic hydrogen centre has been observed. From the ESR spectrum it was described to be a (LiH) + molecule occupying a cation site with a Li + –H 0 separation of 1.44 Å. Below 70 K it is frozen‐in along [111], at higher temperatures it undergoes a rapid reorientational motion. Using ENDOR now the shf interactions of the hydrogen electron with three equivalent Cl and one Li neighbour nuclei are determined precisely at 25 and 41 K and the ESR analysis essentially is confirmed. A theoretical calculation of the shf interactions shows, however, that the centre is not a (LiH) + molecule. It is rather a perturbed interstitial atomic hydrogen centre (H   i 0 (Li) centre) with a Li + –H 0 separation of 2.17 Å, where the hydrogen atom is displaced from the interstitial site by about \documentclass{article}\pagestyle{empty}\begin{document}$ (1/4)\sqrt 3 d_0 $\end{document} d 0 ( d 0 lattice spacing) towards the cation site.