Deuteron NMR spectra of ND4ClO4 single crystal at low temperatures.
2H NMR spectra of ND4ClO4 single crystal were obtained at v0 = 44 MHz. Orientation and temperature (1.9-75 K) dependences were measured. Fitting the spectra gives the effective quadrupole coupling constants for all deuterons and the ground torsional level structure. The isotope reduction of the (A-T) and (A-E) tunnelling splittings, i.e., the ratios of the respective splittings for NH4+ and ND4+, were found to be different. The splittings at T = 24 K are about 60% of the helium temperature values. The spectrum undergoes intermediate narrowing by reorientations between 26 and 34 K and tunnelling related features in the spectra are eradicated. After reaching the extreme narrowing limit, a doublet with gradually decreasing separation was observed, what was attributed to averaging by torsional oscillations of increasing amplitude. At high temperatures (T > 75 K), the narrow spectrum reflects fast multiaxial reorientation of the ammonium ion.
PMR spectroscopy of the tunneling ammonium ion: Generalized line shape theory and some experimental examples
The site symmetry of the NH4+ ion is low in many crystal structures of ammonium compounds. This renders inadequate the commonly considered theoretical models of the tunnel‐split ground librational state of NH4+, which are based on a perfectly tetrahedral crystal field due to assumption of equivalent threefold, and neglect of twofold, axes of symmetry. A general treatment of the NMR line shape theory is therefore considered and Hamiltonian matrix elements for tunneling are explicitly calculated in terms of the seven overlap‐integral parameters related to the four C3– and three C2–symmetry axes of a tetrahedron. The model allows us to discuss all possible ground torsional level structure of the tunneling ammonium ion. The proton NMR line shapes are calculated for all representative cases, and the results are used in comparison with experimental data to elucidate the ground torsional level structures of NH4VO3, (NH4)2ZrF6, (HN4)2TiF6, (NH4)2TeO4, and (NH4) IO4.
The Need For A Sacred Science
The meaning of a science rooted in the sacred, its contrast to modern science and its pertinence to us today.