Atomic hydrogen and muonium in alkali halides

Atomic hydrogen can be trapped at interstitial and substitutional cation and anion sites in alkali halides. The geometrical structure of these defects was established by electron nuclear double resonance (ENDOR). From the analysis of the ENDOR spectra also detailed information was obtained on the electronic structure. In this article the major experimental and theoretical results for atomic hydrogen in several alkali halides are briefly reviewed. Special emphasis is given to the isotope effects upon replacing hydrogen by deuterium. The nature of the dynamical hyperfine and superhyperfine interactions is discussed. Its magnitude to be expected for muonium is estimated. Recent results on muonium centres are discussed on the basis of the knowledge about the hydrogen centres.