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 (Δv/ΔT) 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 Δv/ΔT in this study with the geometrical properties of each host water cage, and these comparisons suggest that the geometry of host water cages affects Δv/ΔT.