Ion and solvent dynamics in aqueous tetramethylammonium chloride solutions

Abstract

It has been demonstrated using isotopic substitution that the distinct inelastic and quasielastic incoherent neutron scattering spectra from N(CH₃)⁺₄ions and the water in liquid and frozen solutions of tetramethylammonium chloride can be identified. The salt is weakly ‘structure-making’, as may be seen from the small changes in water spectrum with concentration. The intraionic torsional modes persist in solution. Their response and that of the highly overdamped but persistent whole-ion librations as well as the translational and rotational diffusion constants allow this tendency to be quantified. The observed effects show that this ion is a useful probe for ‘structure-making’ conditions, e.g. at charged interfaces.