Reorientational Motions in Crystalline (CH₃)₃NHCl, Studied by Raman Spectroscopy

Abstract

Abstract The IR and Raman vibrational spectra of crystalline (CH 3 ) 3 NH + X − (X = Cl, Br, I) are recorded. A complete assignment of the measured frequencies to the internal vibrational modes of the (CH 3 ) 3 NH + cation in the three compounds is obtained. Above the phase transition of (CH 3 ) 3 NH + Cl − (at 308 K) a reorientational motion of the cation around its threefold axis is deduced from the Raman spectrum. This motion is studied by a line shape analysis of the degenerate ν CN (E) vibration. A rotational diffusion constant D ∥ = (0.38 ± 0.05) · 10 12 sec −1 is deduced in agreement with quasielastic neutron scattering results.