Raman Spectroscopy of Nitrogen Clathrate Hydrates

Phase transitions in natural C-O-H-N-S fluid inclusions - implications for gas mixtures and the behavior of solid H2S at low temperatures

C-O-H-N-S-bearing fluids are known as one of the most challenging geochemical systems due to scarcity of available experimental data. H₂S-rich fluid systems were recognized in a wide array of world-class mineral deposits and hydrocarbon reservoirs. Here we report on a nature of low-temperature (T ≥ -192 °C) phase transitions observed in natural CH₄-H₂S-CO₂-N₂-H₂O fluid inclusions, which are modeled as closed thermodynamic systems and thus serve as natural micro-laboratories representative of the C-O-H-N-S system. For the first time, we document solid-solid H₂S (α ↔ β ↔ γ) transitions, complex clathrates and structural transformations of solid state H₂S in natural inclusion gas mixtures. The new data on Raman spectroscopic features and a complete sequence of phase transition temperatures in the gas mixtures contribute to scientific advancements in fluid geochemistry. Enhanced understanding of the phase equilibria in the C-O-H-N-S system is a prerequisite for conscientious estimation of P-T-V-X properties, necessary to model the geologic evolution of hydrocarbon and mineral systems. Our findings are a driver for the future research expeditions to extraterrestrial H₂S-rich planetary systems owing to their low temperature environments.

Thermodynamic Stability of Structure II Methyl Vinyl Ketone Binary Clathrate Hydrates and Effects of Secondary Guest Molecules on Large Guest Conformation

Clathrate hydrates have received massive attention because of their potential application as energy storage materials. Host water frameworks of clathrate hydrates provide empty cavities that can capture not only small molecular guests but also radical species induced by γ-irradiation. In this work, we investigated structure II methyl vinyl ketone (MVK) binary clathrate hydrates with CH₄, O₂, and N₂ and the effects of secondary guest species on MVK conformation in the cavity of hydrate and on the thermodynamic stability of unirradiated and γ-irradiated hydrate phases. The present findings provide meaningful information to understand the nature of guest-host interactions in γ-irradiated clathrate hydrates and to open up practical applications for hydrate-based nanoreactors.