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

Go Fuseya,Satoshi Takeya,Akihiro Hachikubo

doi:10.1039/d0ra06668k

Abstract

C–H symmetric stretching vibrational frequencies of CH4, C2H4 and C2H6 molecules encapsulated in 512, 51262 and 51264 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 CH4, C2H4 and C2H6 molecules encapsulated in sII 51264 cages were smaller than those for molecules in sI 51262 cages, although sI 51262 cages are smaller than sII 51264 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.

Highlights

Clathrate hydrates, commonly known as gas hydrates, are crystalline inclusion compounds consisting of guest molecules of suitable sizes and shapes encapsulated in well-de ned cages formed by water molecules
We revealed that Dv/DT depends on the geometry as well as the volume of host water cages
We investigated the slopes of C–H symmetric stretching vibrational frequencies under changing temperatures (Dv/DT) for various hydrocarbon molecules in 512, 51262 and 51264 cages of structure I (sI) and structure II (sII) hydrates

Summary

Introduction

Commonly known as gas hydrates, are crystalline inclusion compounds consisting of guest molecules of suitable sizes and shapes encapsulated in well-de ned cages formed by water molecules. We observed the variations in the Raman shi of C–H symmetric stretching vibrations for various guest hydrocarbon molecules in sI 512 and 51262 cages and in sII 512 and 51264 cages under changing temperatures.

Results

Conclusion