Deuteron NMR spectra of NH3D+ Ions

A theory of deuteron nuclear magnetic resonance (NMR) spectra is outlined for NH3D+ ions. Dipolar interactions among all five spins in the ion contribute to the shape of the deuteron spectra. Dimensions of the ammonium ion can be derived from the structure of the single-crystal spectra. The analysis of the spectra supplies ways to distinguish between cases of rigid, tunnelling or reorienting protons. Single-crystal spectra of partially deuterated ammonium perchlorate measured at 5 K provide examples of the applicability of the theory. Distances between nuclei are derived. Evidence is provided for tunnelling and reorientation of protons in NH3D+ ions. Deuteron spectra indicate that NH3D+ ions exhibit a diverse mobility. There exist ions with immobile deuterons which populate one position in the crystal unit cell (isotopic ordering), while the deuterons in the remaining ions reorient about C3 axes parallel to the N-D bond orientation of the rigid ones. The contribution of the latter increases with increasing temperature.