Spin–lattice relaxation study of protons of some N2H 2+6 salts

Abstract

The spin–lattice relaxation times of protons in polycrystalline hydrazine dichloride, N₂H₆Cl₂, hydrazine dinitrate, N₂H₆(NO₃)₂, hydrazine hydrate, N₂H₆O, and hydrazine sulphate, N₂H₆SO₄, have been measured at 60 MHz as a function of temperature between 140 and 450 K. T₁ passes through a minimum of 21.6 ms for each of the first three compounds. However, T₁ for hydrazine sulphate exhibits anomalous behaviour at low temperatures: it usually passes through a minimum of 47 ms but in some experiments through a minimum of 27 ms. The temperature dependence of T₁ was found to be characteristic of a dominant relaxation mechanism, reorientational motion of NH⁺₃ groups about the N—N bond direction. The experimental value (T₁)_min= 21.6 ms agrees exactly with the estimated value for the first three compounds. However, all the experimental T₁ results cannot be fitted by assuming an Arrhenius dependence of correlation times and this has been attributed to a decrease in activation energies with increasing temperature.