Laser micro Raman investigations on gas hydrates

Abstract

Laser Raman spectroscopic measurements for some hydrocarbon gas molecules (propane and methane) have been reported on laboratory-synthesized hydrates in India. Our results corroborate the literature data, thus providing good laboratory standards. Such measurements are vital while analysing natural samples, where the guest molecules could be methane, ethane, propane, etc. The present results also demonstrate that the Raman mode around 60 cm-1 is a characteristic feature for structure-II hydrates. Gas hydrates with mixed guest molecules (tetrahydrofuran (THF) and methane) were also probed by Raman spectroscopy. The observed Raman spectra clearly indicate that the methane molecules occupy smaller cages upon using THF and water in 1:17 mol ratio. However, the Raman signatures for both large and small cages, in structure-II, are clearly seen using water mixed with lesser amount of THF.