Nuclear spin relaxation and molecular motion in liquid and solid phosphine

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Abstract
Extensive measurements of the nuclear magnetic resonance relaxation times are reported for the proton, deuteron and phosphorus-31 resonances in a series of solutions of phosphine (PH3) in perdeuterophosphine (PD3) in the liquid and in the solid plastic crystal phase. All these measurements are interpreted in a consistent manner in terms of the molecular motion in spite of the difficulties arising from the proton/deuteron exchange. It is found that both the molecular reorientation and translation are rapid in the liquid. On solidification to the plastic crystal phase the molecular reorientational motion is little affected and is possibly more rapid than in the liquid but the translational motion is much slower. Correlation times are obtained for reorientation, molecular angular velocity and translational motion as well as estimates of the self-diffusion constant in the two states. Independent estimates of the molecular reorientational and angular velocity correlation times have been obtained. Since they are comparable in magnitude only a partial test of the Hubbard relation could be made. The 31P relaxation time is spin-rotation controlled in the solid plastic crystal phase and this is the first time this has been established for this nucleus.