Spin-lattice relaxation in liquid phosphorus tribromide

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Abstract
The 31P spin-lattice relaxation time has been measured at 9 Mhz and 18 Mhz in liquid PBr3 as a function of temperature from -80°c to +180°c. The relaxation time T 1ρ in the rotating frame has also been measured from -80°c to room temperature at a Larmor frequency of 14·3 Mhz and a rotating field strength of 5·4 gauss. The 31P spin-lattice relaxation time is controlled by the spin-rotation interaction at high temperatures and a scalar interaction with the bromine at low temperatures which endows T 1 with a frequency dependence. Both a maximum and a minimum in T 1 are found at 9 Mhz. The relaxation time T 1ρ is controlled entirely by the scalar interaction over the whole temperature range. From the results we have separated the contributions to T 1 as a function of temperature from the three relaxing mechanisms, the direct dipolar, the spin-rotation and the scalar interaction and their corresponding correlation times. The correlation time for the scalar interaction is the bromine spin-lattice relaxation time. The scalar coupling constants between 31P and the 81Br and 79Br nuclei are found to be 380 hz and 350 hz respectively and the spin rotation constant of the 31P nucleus in PBr3 is found to be about 7·6 khz. The quadrupole coupling constants for the 81Br and 79Br are estimated to be 200 Mhz and 230 Mhz respectively.