Effect of molecular reorientation in urea on the 14N PNQR linewidth and relaxation time

The theory of the influence of molecular C=O reorientation in urea on the 14N PNQR linewidth and spin-lattice relaxation time is presented. Pulse techniques are used to measure the inverse linewidth, spin phase memory time and spin-lattice relaxation time of the two high frequency transitions at several temperatures. The relaxation time T1z of the low-lying transition is measured using double radiation methods. At room temperature the spin-lattice relaxation times are highly anisotropic, with T1z three orders of magnitude shorter than T1x and T1y. The experimental results are consistent with a molecular C=O reorientation. The activation energy for this motion is ΔE=11.7±2 kcal/mole.