Precise determination of the 13C nuclear magnetic moment from 13C, 3He and 1H NMR measurements in the gas phase

Abstract

NMR spectroscopy was applied for the precise determination of the 13C nuclear magnetic dipole moment on the basis of new results available for nuclear magnetic shielding in methane and helium-3. For this purpose small amounts of 13CH 4 and 3He as the solutes were observed in CO 2 or Xe as the gaseous solvents by 13C, 3He and 1H NMR spectra at the constant external field, B 0 = 12.7586 T. In every case the measured resonance frequencies ( ν C, ν He and ν H) were linearly dependent on the density of solvent. It allowed us the evaluation of the above frequencies free from intermolecular interactions after the extrapolation of experimental points to zero-density of gaseous solvents. Combining these measurements with the relevant value of 13C shielding in methane it was possible to determine the 13C nuclear magnetic moment with much better precision than before, μ( 13C) = 0.70236944(68) μ N. Application of new theoretical results for carbon shielding in the methane molecule permitted similar evaluation of the 13C nuclear magnetic moment, it shows that the experimental and theoretical results are consistent and the new 13C magnetic moment can be efficiently applied in the field of NMR spectroscopy.