Incoherent, inelastic neutron scattering has been used to study the vibrational spectra of tetramethylammonium montmorillonite and trimethylammonium vermiculite in the energy range 20–140 meV. For both systems peaks are observed due to the internal modes of the intercalate and to the excitations of the hydroxyl groups within the host layers. For the montmorillonite sample, it is found that the steric constraints imposed on the tetramethylammonium ion by the bounding clay layers contribute an additional 28 meV to the rotational barrier of the methyl groups. This additional barrier is shown to be strongly related to the volume that the tetramethylammonium ion occupies. For the trimethylammonium vermiculite sample normal mode analysis of the internal modes of the intercalated ion shows that the N-H bond is parallel to the c-axis of the host.