Optical and EPR investigations of a new hydrogen center in potassium chloride

Abstract

In KCl interstitially diffusing neutral hydrogen atoms (H ⁰ _i ) can be trapped near substitutional Li⁺ ions. The new center possesses a characteristic absorption band at 250nm, at the long wavelength side of the knownH ⁰ _i absorption band (235nm). EPR measurements reveal, that the hydrogen atoms are closely connected to the Li⁺ ions at a cation lattice site forming (LiH)⁺ molecules. Below 70K hydrogen and lithium occupy a fixed relative position to each other in a (111) crystal direction: the hydrogen shows a superhyperfine interaction to three equivalent Cl⁻ neighboring ions. Above 70K the hydrogen exhibits a superhyperfine interaction to six equivalent chlorine neighbors, interpreted by a rapid reorientational motion of the (LiH)⁺ molecule within the cation vacancy. The high temperature interaction parameters can be explained as the time average of the low temperature values. A qualitative explanation of the optical absorption of the (LiH)⁺ center is given.