SIMULATION OF COLLECTIVE DYNAMICS OF N-NONADECANE IN THE UREA INCLUSION COMPOUND

Collective translational vibrations of n-nonadecane molecules incorpor ated within the channels of urea inclusion compounds are investigated at 180K by molecular dynamics simulation. Incoherent inelastic neutron scattering (INS) profiles are calculated from the simulation trajecto ries and compared to experiment. The results allow interpretation of t he peaks in the low-energy INS spectrum. Intermolecular intrachannel v ibrations of the guest n-nonadecane molecules along the channel axis g ive rise in the simulation to a peak in the density of states at appro ximate to 20 cm(-1), the cutoff frequency of the corresponding longitu dinal acoustic mode propagating along the channel axis. This is assign ed to the experimental peak at approximate to 23 cm(-1). At lower wave numbers a peak in the dynamic structure factor arises from the relati ve displacements of host and guest substructures (i.e., the rigid-body sliding of the array of alkane molecules within the channels).