Absence of fast H+-ion motion in aqueous HCl. A neutron scattering study

Abstract

The quasielastic scattering of neutrons on four aqueous HCl solutions with HCl concentrations of 2.79, 5.19, 784 and 10.03 mol kg^–1) has been studied at room temperature. The measurements were performed with incident neutrons of wavelength 9.043 Å. From the primary scattering data the intermediate scattering law I(k,t) was calculated for a certain set of momentum transfers. In all cases I(k, t) was found to be a single exponential yielding the mean proton self-diffusion coefficient which as a macroscopic quantity is also known from other sources. From this finding it follows that D⁺, the local self-diffusion coefficient of the proton in the state H⁺ ion, must also have the same value as the mean proton self-diffusion coefficient in the solution which is lower than that of pure water.