Deuteron NMR spectra of ammonium ion isotopomers at low temperatures

Abstract Partially deuterated ammonium compounds contain ammonium ion isotopomers with relative abundances given by the binomial distribution of protons and deuterons. All isotopomers with deuterons contribute characteristic deuteron NMR spectra at 5 K. Experimental NMR spectra were separated and respective contributions of isotopomers were determined. The derived contributions agree with expected values for a given deuteration in the case of ammonium hexafluorophosphate. In ammonium hexachlorotellurate both NH 2 D 2 + and about 50% of NH 3 D + ions are rigid, while the remaining NH 3 D + perform limited jumps. NHD 3 + and ND 4 + ions undergo tunnelling rotation, NH 3 D + ions perform either jumps about C 2 axis or limited jumps, but some stay rigid in ammonium hexachlorostannate. NH 2 D 2 + , NHD 3 + and ND 4 + undergo rotational tunnelling. In the case of ammonium perchlorate, the NH 3 D + ions perform either jumps about C 3 axis or limited jumps whilst some remain rigid. Very low values of activation energies were derived for all spectral components from the temperature dependence of their spectra, up to about 20 K, which indicates an incoherent tunnelling nature of the observed dynamic processes. The diverse mobility of NH 3 D + ions appears to be the most interesting and new feature.