Deuteron NMR spectra of ND 4ClO 4 single crystal at low temperatures

Abstract

2H NMR spectra of ND 4ClO 4 single crystal were obtained at ν 0 = 44 MHz. Orientation and temperature (1.9–75 K) dependences were measured. Fitting the spectra gives the effective quadrupole coupling constants for all deuterons and the ground torsional level structure. The isotope reduction of the (A-T) and (A-E) tunnelling splittings, i.e., the ratios of the respective splittings for NH 4 + and ND 4 +, were found to be different. The splittings at T = 24 K are about 60% of the helium temperature values. The spectrum undergoes intermediate narrowing by reorientations between 26 and 34 K and tunnelling related features in the spectra are eradicated. After reaching the extreme narrowing limit, a doublet with gradually decreasing separation was observed, what was attributed to averaging by torsional oscillations of increasing amplitude. At high temperatures ( T > 75 K), the narrow spectrum reflects fast multiaxial reorientation of the ammonium ion.