14N Nuclear Quadrupole Resonance Study of Hydrogen Bonding in NH3·12H2O

The four‐line ¹⁴N nuclear quadrupole resonance spectrum in the ammonia hydrate ${\mathrm{NH}}_3·\frac{1}{2}{\mathrm{H}}_2\mathrm{O}$ is reported. The frequencies were unambiguously paired by their Zeeman behavior and each pair is assigned to respective inequivalent sites in the crystal lattice. The temperature dependence was measured between 77°K and the melting point; it is quantitatively interpreted in terms of a motional averaging theory corrected for volume effects. The same theory is applied to previous results on NH₃ and ND₃, and the quasistatic coupling constants are recalculated. Solid‐state shifts of NH₃ in the pure ammonia lattice and in the two inequivalent lattice sites of the hydrate are thus obtained and interpreted in terms of the three different hydrogen‐bonding situations.