Incoherent Neutron Scattering Study of Proton Motions in Solid HCl

Incoherent neutron scattering from protons in HCl has been measured mainly in Phase I with the disordered structure of molecular orientation. The observed energy spectra of neutrons are well interpreted by a reorientational jump model in which a molecule makes reorientation among twelve <110> directions through the 60° and 90° flipping processes. The residence time τ between successive jumps obtained by the model-fit obeys the relation τ=τ 0 exp ( E / k B T ) with τ 0 =1.07×10 -12 sec. and E =0.372 kcal/mol. in the higher-temperature region in Phase I. The value of τ was compared with the correlation time for molecular reorientation obtained by NMR method.