Inelastic coherent neutron scattering on TBBA in the low temperature phases

Abstract
Inelastic coherent neutron scattering experiments have been performed on a nondeuterated single crystal of TBBA which is transformed by melting into a single smectic domain. Despite the strong incoherent background, it was possible to determine several acoustic longitudinal and transverse dispersion branches in three phases : solid (VIII), smectic B (V) and smectic VI. The transverse mode (rigid layer mode) propagating perpendicular to the layers of molecules has been observed in the solid phase (0.15 THz at the zone boundary), while in the smectic B phase, this mode could no longer be resolved. The experiment was not performed for the smectic VI mesophase