ENDOR Investigation of Cu++ Centres in NH4Cl I. Experimental Results

Abstract
Two Cu++ centres in NH4Cl single crystals grown from acid (I) and neutral (II) aqueous solution were investigated by ESR and ENDOR at 4.2 °K. From the superhyperfine and quadrupole data obtained for several shells of neighbour nuclei the following centre models are proposed: in both centres Cu++ is at an interstitial site with 2 NH4+ vacancies along [001] at both sides of the Cu++. In centre I the vacancies are filled by H2O, in centre II by NH3. The precise configuration of the H2O and NH3 molecules could be determined.