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

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.