Temperature effects on the C-H symmetric stretching vibrational frequencies of guest hydrocarbon molecules in 5 12 , 5 12 6 2 and 5 12 6 4 cages of sI and sII clathrate hydrates.

C-H symmetric stretching vibrational frequencies of CH 4 , C 2 H 4 and C 2 H 6 molecules encapsulated in 5 12 , 5 12 6 2 and 5 12 6 4 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 v /Δ T ) for CH 4 , C 2 H 4 and C 2 H 6 molecules encapsulated in sII 5 12 6 4 cages were smaller than those for molecules in sI 5 12 6 2 cages, although sI 5 12 6 2 cages are smaller than sII 5 12 6 4 cages. We compared the results of Δ v /Δ T 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 v /Δ T .