Lattice dynamics of a rotor-stator molecular crystal: Fullerene-cubaneC60⋅C8H8

International audienceThe dynamics of fullerene-cubane C 60 ·C 8 H 8 cocrystal is studied combining experimental x-ray diffuse scattering, quasielastic and inelastic neutron scattering INS and simulation molecular dynamics investigations. Neutron scattering gives direct evidence of the free rotation of fullerenes and of the libration of cubanes in the high-temperature phase, validating the " rotor-stator " description of this molecular system. X-ray diffuse scattering shows that orientational disorder survives the order/disorder transition in the low-temperature phase, although the loss of fullerene isotropic rotational diffusion is featured by the appearance of a 2.2 meV mode in the INS spectra. The coupling between INS and simulations allows identifying a degeneracy lift of the cubane librations in the low temperature phase, which is used as a tool for probing the environment of cubane in this phase and for getting further insights into the phase transition mechanism