[PPS09-P05] Variation of carbon isotopic composition with formation of CO2 clathrate hydrate
Keywords:Amorphous ice, Clathrate hydrate, Infrared spectroscopy, Isotope
Amorphous ice including 12CO2 and 13CO2 was prepared with vapor deposition of mixture of 12CO2, 13CO2 gases and distilled and degassed water on a substrate of oxygen-free copper at 42 K. In the gas mixture, the 12C/13C isotopic ratio was 92, and (12CO2 +13CO2)/ H2O was 1.4. The total pressure in the vacuum chamber was kept at about 3.5 × 10–5 Pa during the deposition. After the deposition of amorphous ice, the substrate was warmed to 180 K at a rate of 1–4 K/min. The IR spectra were measured using a spectrometer (Shimadzu IRPrestage-21) at 2 K intervals during warming. To analyze the sublimation behaviors, the temperature programed desorption (TPD) curves were also measured using quadrupole mass spectrometer (Pfeiffer QME220) during warming.
From the analyses of the wave numbers of the O–H stretching modes of H2O, 12C=O asymmetric stretching mode of 12CO2, and 13C=O asymmetric stretching modes of 13CO2 during the warming, remarkable changes were found at around 100 K. From the TPD curve, furthermore, a remarkable gas release was observed at this temperature. Because of the closed wave number of the 12C=O asymmetric stretching mode at 100 K with that of CO2 clathrate hydrate , the formation of CO2 clathrate hydrate at 100 K was confirmed. It was found that the 12CO2/13CO2 ratio increases at around 100 K. These results suggest that the formation of clathrate hydrate from amorphous ice with warming can be a cause of 12C condensation.
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