Temperature effects on the C-H symmetric stretching vibrational frequencies of guest hydrocarbon molecules in 5, 56 and 56 cages of sI and sII clathrate hydrates.

C-H symmetric stretching vibrational frequencies of CH, CH and CH molecules encapsulated in 5, 56 and 56 cages of structures I (sI) and II (sII) clathrate hydrates measured by Raman spectroscopy in the temperature range of 93-183 K was analysed. The slopes of the symmetric stretch vibrational frequencies under changing temperatures (Δ/Δ) for CH, CH and CH molecules encapsulated in sII 56 cages were smaller than those for molecules in sI 56 cages, although sI 56 cages are smaller than sII 56 cages. We compared the results of Δ/Δ in this study with the geometrical properties of each host water cage, and these comparisons suggest that the geometry of host water cages affects Δ/Δ.