Neutron scattering study and lattice dynamical simulation of clathrate H2O+He

The vibrational dynamics of clathrate hydrate H2O + He formed under pressur e of He gas at 3.6 kbar was studied in situ using an inelastic neutron scat tering technique. The comparison of the measured spectrum with that of ice II obtained previously in similar conditions showed that the two spectra ar e almost identical in both translational and librational regions. Based on the lattice dynamical model for ice II (Dong, Wang, Kolesnikov, Li, J. Chem . Phys. 109 (1998), 235) the clathrate hydrate spectrum was calculated by i ntroducing an additional Van der Waals interaction between the water molecu le and the helium atom. Results indicate that the interaction between water and guest molecules is too weak to affect the vibrational dynamics of ice II host lattice. (C) 1999 Elsevier Science B.V. All rights reserved.