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

Abstract

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 T_1z of the low‐lying transition is measured using double radiation methods. At room temperature the spin‐lattice relaxation times are highly anisotropic, with T_1z three orders of magnitude shorter than T_1x and T_1y. The experimental results are consistent with a molecular C=O reorientation. The activation energy for this motion is ΔE=11.7±2 kcal/mole.