Molecular dynamics simulations of clathrate hydrate. Intramolecular vibrations of methane

Intramolecular vibrational spectra of methane in clathrate hydrate structure I were obtained by molecular dynamics simulations using the Kumagai, Kawamura, and Yokokawa (KKY) potential model that allows unconstrained atomic motions. Peak frequency shifts between the power spectra of methane molecules in large and small cages were found in the GH stretching (υ(l), υ₃) modes, in contrast no frequency shifts were observed in the H-C-H bending (υ₂, υ₄) modes. We discuss an interaction between water and methane molecules from these frequency shifts and the GH distance depending on the cage size. An understanding of the interaction between guest and host molecules helps us to clarify the formation and dissociation processes of clathrate hydrates.