Temperature effects on the C-H symmetric stretching vibrational frequencies of guest hydrocarbon molecules in 512, 51262and 51264cages of sI and sII clathrate hydrates

Abstract

C-H symmetric stretching vibrational frequencies of CH4, C2H4and C2H6molecules encapsulated in 512, 51262and 51264cages 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 CH4, C2H4and C2H6molecules encapsulated in sII 51264cages were smaller than those for molecules in sI 51262cages, although sI 51262cages are smaller than sII 51264cages. We compared the results of Δv/ΔTin 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.