Raman spectra of gas hydrates—differences and analogies to ice 1h and (gas saturated) water

Raman spectroscopic investigations on natural samples from the Integrated Ocean Drilling Program (IODP) Expedition 311: Indications for heterogeneous compositions in hydrate crystals

“…These maps exhibit clearly a relative enrichment of H 2 S in some parts of the mapped surface of the polycrystal. In contrast, DSC measurements on homogeneous gas hydrates which were synthesized from ice and a H 2 S-CH 4 -gas mixture result in only one dissociation peak at 236.7 ± 1.2 K [19]. These results support the assumption of coexistence of various gas hydrate phases with different compositions in the natural sample.…”

“…These results support the assumption of coexistence of various gas hydrate phases with different compositions in the natural sample. Experimental studies with CH 4 -H 2 S mixtures confirmed that the relative composition of CH 4 -H 2 S in the hydrate phase corresponds to the feed gas composition upon hydrate formation [19], so it is reasonable to assume that the growth of the hydrate studied in this research was fed by gas with a fluctuating composition of H 2 S and CH 4 over temporal and/or spatial scale.…”

Spectroscopic Signatures of Halogens in Clathrate Hydrate Cages. 2. Iodine

“…The band changes its shape and position upon freezing, as was previously observed. 20 One final observation is worth mentioning. When the rose iodine doped THF clathrate samples were cooled to liquid nitrogen temperatures, they changed to pale yellow.…”

“…One possibility is that the iodine interacts more strongly than expected with the oxygen atoms. Recent calculations by Schofield and Jordan 30 of the Cl 2 -(H 2 O) 20 cluster, which mimics Cl 2 in the 5 12 cage, indicate that the hydrogen bonding in a 5 12 cage does not eliminate the ability of the oxygen atoms to donate electron density to the σ* orbital on a chlorine molecule. The chlorine prefers to align on an axis between two oxygen atoms.…”

“…We acknowledge discussions with Drs. Ramon Henrnandez and Nadine Halberstadt regarding their calculation of the electronic spectrum of the H 2 O-Br 2 dimer and Daniel Schofield and Kenneth Jordan for preliminary communication of their ab initio results for chlorine in (H 2 O) 20 and (H 2 O) 24 cages.…”