Raman spectra of gas hydrates - differences and analogies to ice 1h and (gas saturated) water

It is generally accepted that Raman spectroscopic investigations of gas hydrates provide vital information regarding the structure of the hydrate, hydrate composition and cage occupancies, but most research is focused on the vibrational spectra of the guest molecules. We show that the shape and position of the Raman signals of the host molecules (H2O) also contain useful additional information. In this study, Raman spectra (200-4000cm(-1)) of (mixed) gas hydrates with variable compositions and different structures are presented. The bands in the O-H stretching region (3000-3800cm(-1)), the O-H bending region (1600-1700cm(-1)) and the O-O hydrogen bonded stretching region (100-400cm(-1)) are compared with the corresponding bands in Raman spectra of ice Ih and liquid water. The interpretation of the differences and similarities with respect to the crystal structure and possible interactions between guest and host molecules are presented. (c) 2005 Elsevier B.V. All rights reserved.