Inelastic neutron scattering studies and barriers to methyl rotation in alkali-metal methanesulphonate salts

Abstract

The “torsional” motion in the methanesulphonate ion (CH₃SO₃^–) in its alkali-metal salts has been investigated by means of incoherent inelastic neutron scattering spectroscopy. Infrared and Raman spectra in the low-frequency region were also obtained to aid in assigning torsional modes. The Cs⁺ salt shows a single torsional band, while the other salts show several bands which may be assigned to torsions. A model which takes account of the coaxial motions of the SO₃ and CH₃ groups has been used to calculate values for the sum of the internal and external barriers which hinder reorientation of the CH₃ group.