Researching carbon dioxide hydrates in thin films via FTIR spectroscopy at temperatures of 11–180 K

The IR spectra of thin films of a mixture of carbon dioxide and water were obtained using the physical vapor deposition method. They were researched in the temperature range of 11–180 K. Based on the results of the research; the formation of hydrates and clathrates was investigated. Several methods were used in the course of this research. These methods are mass spectroscopy, IR spectroscopy, and optical analysis of the thin films formed. Not only the molecular composition but also the state of the structure of molecular mixtures can be determined via Fourier transform infrared spectroscopy (FTIR). Additional data were needed to confirm the emergence of certain structures of carbon dioxide and water mixtures. The mass spectroscopy method and interference pattern analysis were utilized to obtain that data. Hydrate and gas hydrate structures of CO2 do form in the mixture of carbon dioxide and water. This was confirmed in the course of the experiments. The CO2 molecules are contained in their structures by the hydrate compounds formed, which prevents CO2 from sublimating at the sublimation temperature of free CO2 (93 K) under the pressure of P = 0.5 μTorr. Meanwhile, the sublimation temperature of CO2 molecules bound in hydrate structures becomes equal to 147–150 K. The ratio of CO2 and H2O concentrations was chosen to be 25 % and 75 %, respectively. For this ratio, the changes in the spectra and the results obtained via mass spectroscopy indicate incomplete hydration of the mixture. Still, some CO2 molecules remain free and sublimate at a lower temperature. It was found that the concurrent increase in the refractive index and decrease in the concentration of H2O from 100 % to 25 % indicate the growth of the formations that are less dense compared with the amorphous structures of CO2 and H2O condensates. The results obtained in the course of this research broaden the knowledge of the processes of clathrate and hydrate formation in mixtures of CO2 and H2O, the physical characteristics of their structures, and the changes in their characteristics depending on the way they are formed.