CH3 Rotational Tunnelling in Alkali Acetates and Correlation between NMR Spin-Lattice Relaxation and Neutron Scattering Data

A.-S. Montjoie, W. Miiller-Warmuth
1985 Zeitschrift fur Naturforschung A-A Journal of Physical Sciences  
NMR spin-lattice relaxation rates l / T1 have been measured at 15 and 30 MHz and various temperatures in polycristalline sodium and potassium acetate. The results for CH3COONa are characteristic of methyl group tunnelling with a frequency which is very much larger than the NMR Larmor frequency. Derived values of the torsion energy (1.1 kJ/mol) and the ground state tunnel splitting (5.6 meV) agree with data obtained from inelastic neutron scattering by Clough et al. The shape of the hindering
more » ... of the hindering potential and the activation energy for classical reorientation (3.2 kJ/mol) have been determined. Since the relaxation rate of CH3COOK is a superposition of at least two mechanisms, in this case the results are less accurate and refer to one type of CH3 rotor only: activation energy 5.4 kJ/mol, tunnel splitting 0.23 meV. Comparison is made between tunnel splittings and classical activation energies for the acetates and various other materials: strong correlations are demonstrated and discussed.
doi:10.1515/zna-1985-0610 fatcat:3zciu7kbnfgd7k3x5hwyn7gvvu