Nuclear Resonance in Solid Nitrogen Trifluoride

A combined NQR and NMR study has been made of solid NF3. The quadrupole coupling constant and asymmetry parameter of 14N have been determined and the low-temperature torsional oscillation frequencies of the molecule in the solid calculated by fitting the temperature dependence of the resonance frequencies to Bayer theory. The constants obtained are: 3e2q0Q/4h = 5.3012±0.0005×106 sec−1, η0 = 0.00112±0.00002, vx = 1.505±0.005×1012 sec−1 and vy = 1.003±0.003×1012 sec−1, respectively, where the first two parameters are for the rigid lattice at 0°K. Above about 35°K, and particularly near the phase transition at 56.6°K, Bayer theory is inadequate to explain the observed temperature dependence. The linewidth of the 19F magnetic resonance undergoes a precipitous decrease above 35°K and becomes very narrow before the solid melts. A consistent interpretation of the data may be made if one assumes the onset of hindered rotation of the NF3 molecule about its triad axis below the transition temperature and the occurrence of additional large amplitude motions above the transition, but this speculation requires further proof.