Molecular reorientations of 1-chloroadamantane in its plastic solid phase

Using the incoherent quasielastic neutron scattering technique, we have studied the molecular reorientations of 1-chloroadamantane C10H15Cl in its plastic phase. The measurements were done in a temperature range from 246 K to 403 K, with two values of incoming neutron wavelength, namely 9 Å and 8 Å, using a powder sample. It is shown that molecular motions consist of reorientational jumps between twelve equilibrium positions equally spaced by 30° around the molecule symmetry axis, together with a tumbling of the molecule from one [100] lattice direction to another. Below the solid-solid transition (T = 244·2 K), only uniaxial 120°-jumps occur, between three equally spaced orientations around the molecular axis.