Spin-lattice relaxation and molecular motion in liquid phosphorus trichloride, phosphorus oxychloride and phosphorus oxyfluoride

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Abstract
The 31P spin-lattice relaxation time has been measured at 9 Mhz in liquid PCl3, POCl3 and POF3 from the supercooled liquid almost to the liquid-vapour critical temperature. The 19F spin-lattice relaxation time has also been measured in POF3. The phosphorus spin-lattice relaxation times for these liquids are believed to be mainly controlled by the spin-rotation interaction. This is the first time as far as we are aware that this has been observed for the 31P magnetic resonance. For phosphorus trichloride the contributions from direct dipolar and spin-rotation interactions to the experimental 31P spin-lattice relaxation times have been separated. Correlation times for molecular reorientation and molecular angular velocity are derived and the 31P spin-rotation constant is estimated to be about 14 khz. The 31P spin-lattice relaxation times can be satisfactorily interpreted in terms of molecular motion parameters evaluated using shear viscosity data. The spin-rotation constant for POCl3 is estimated from the measured 31P spin-lattice relaxation times and viscosity data to be about 18 khz. For liquid POF3 both the 19F and the 31P spin-lattice relaxation times are believed to be mainly controlled by the spin-rotation interaction. A detailed analysis is made of the molecular motion. The spin-rotation constants for the 19F and 31P nuclei are estimated to be about 14 khz and 24 khz respectively.