Nitrogen-14 Nuclear Quadrupole Resonance Study of Lithium Hydrazinium Sulfate

Abstract

Nitrogen-14 nuclear quadrupole resonance (NQR) transition frequencies of the NH2 group of the hydrazinium ion in lithium hydrazinium sulfate have been measured as a function of temperature from 4.2 to 360°K. The usual treatment of temperature dependence, which considers the effect on the transition frequencies of molecular oscillations about the principal field gradient axes, is generalized by considering oscillations about an arbitrarily oriented axis system. This generalization leads to the determination of the orientation of the field gradient axes in the NH2 group, and to a clarification of the existing model of the dynamics of the hydrazinium ion. It is found that between 40 and 320°K the NH2 group undergoes small oscillations about the N–N axis whose amplitude increases linearly with temperature. Above 320°K the amplitude of these oscillations increases more rapidly than a linear function. It is also found that above 150°K, proton exchange in the H–N–H plane of the NH2 group takes place rather than rigid rotation of the protons about the bisector of the H–N–H angle. The linear increase of oscillation amplitude with temperature between 40 and 320°K is found to be inconsistent with the Bayer theory, unless and ad hoc assumption is made about the temperature dependence of the oscillation frequencies.