Torsional and librational modes of the monomethylammonium ion, CH3NH +3, in its salts, studied by inelastic neutron scattering

Abstract

This paper reports the direct observation, assignment and study of the torsional and librational vibrations of the ions CH₃NH⁺₃, CD₃NH⁺₃ and CH₃ND⁺₃ in the various phases of their salts with Cl^–, Br^–, I^– and PF^–₆, by inelastic neutron scattering (I.N.S.). From these observations it is possible to derive a value for the torsional frequency of the “free” CH₃NH⁺₃ ion, which is intermediate between that of C₂H₆ and N₂H²⁺₆. It is also possible to calculate the internal and external barriers to rotation of the ion in certain of the lattices.