Dipolar Relaxation of 7Li by Hindered Rotators NDxH3−x in Lithimn Hydrazinium Sulfate.

Abstract

When a hindered rotation does not change the spatial charge distribution but merely permutes the locations of nuclear magnetic moments, the resulting spin-lattice relaxation of a nearby fixed nucleus is likely to be dipolar even if this nucleus has a quadrupole moment. The dipolar relaxation rate is props rtional to the average of γ2I(I + 1) for the rotating nuclei and accordingly varies linearly with percentage of deuteration. For 7Li in LiN2H5SO4 at 14 MHz the peak is 1.8 sec− at 185°K, while in 81% deuterated LiN2D5SO4 it is 4.2 times smaller, as predicted. The ND2 group deuterons also have a peak at this temperature, and all three curves show activation energy of about 0.19 eV, as found previously for protons and deuterons within rotating NH3 and ND3 groups.