Nuclear spin relaxation in molten alkali nitrates

Abstract

The nuclear magnetic relaxation of the 23Na and 87Rb spins in molten NaNO 3 and RbNO 3 was measured. The rates were found to be 19.2 and 670 sec −1 near the melting point and decrease in proportion to the reciprocal temperature. The rates were explained by means of the quadrupolar mechanism, with electric field gradients calculated from a model consistent with the observed field gradient in solid NaNO 3. Calculation of the field gradients around the triangular nitrate ion coupled with X-ray diffraction measurements led to the conclusion that the translational motion of the ions was the most effective relaxation mechanism with a relatively smaller contribution from the rotation of the anion. Under these circumstances the correlation time calculated from our data is the average time that the spatial configuration of a group of near neighbors persists in the liquid state. It was found to be about 8 × l0 −13 sec.