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Study of Chemical Processes in Extraterrestrial Atmospheres
Chudják, Stanislav ; Ferus, Martin (oponent) ; Matejčík, Štefan (oponent) ; Krčma, František (vedoucí práce)
The aim of this work is study of chemical processes in extraterrestrial atmospheres and the synthesis of organic compounds formed in electrical discharges in gaseous mixtures. Presented study focuses on the simulation of the atmosphere of Titan. The most common composition of the gaseous mixture was methane (1-4 sccm) in 200 sccm of nitrogen. Measurements with trace amounts of oxygen and carbon dioxide were also performed. In addition to the composition of the gas mixture, the experiments also varied the value of the electrical power delivered from 2 W - 12 W. The measurements were carried out at laboratory temperature but also at liquid nitrogen temperature, which made the experiment closer to the real conditions on Titan. Identification of the synthesized gaseous products in the reactor was carried out mainly by proton ionization mass spectrometry. Further measurements were using ion mobility spectrometry and Fourier transform infrared spectrometry. The discharge itself was characterised by optical emission spectrometry, confirming the presence of active nitrogen species and radicals arising from methane. In addition, the first negative and nitrogen second positive systems as well as the violet CN radical system were identified in the measured spectra. From the nitrogen second positive system, the rotational temperature was determined to be 2300 2400 K. The vibrational temperature was also determined from this system depending on the concentration of the gas mixture composition from 3100-3400 K. The vibrational temperature was calculated from the nitrogen first negative system, but it decreased slightly with methane concentration and increased with power in the interval from 3950-4350 K. The vibrational temperature obtained for the violet spectral CN system had similar dependence, with values ranging from 5900-7700 K. A number of aliphatic hydrocarbons, some aromatic hydrocarbons and also amino or cyano compounds were detected at laboratory temperature using a PTR-MS. The highest molecular weights at laboratory temperature were up to 150 g.mol-1 with hydrogen cyanide, acetylene or acetonitrile being the most abundant compounds. In measurements at liquid nitrogen temperature, nearly 200 substances up to a molecular weight of 500 g.mol-1 were identified. Even in low temperature measurements, acetonitrile or diacetylene were the dominant substances, but hydrogen cyanide was not so abundant as at ambient temperature. Small amount of oxygen was also used in the measurements and under these conditions, e.g. formamide or acetone were among the significant detected substances. In both laboratory and low-temperature measurements, it was confirmed that with increasing methane concentration, higher molecular weight substances were formed and lower number of simple substances were formed. The same dependence was observed with increasing power delivered to the system. The thesis also includes measurements by ion mobility spectrometry. The most important gas detected was ammonia, followed by propane-2-ol, ethanol and most likely diethylamine. The last measurements were obtained by FTIR. The basic spectrum shows bands belonging to aliphatic hydrocarbons (3050-2800 cm-1) and aromatic compounds (benzene at 1506 cm-1), nitrogen substituted hydrocarbons bands (1350-1600 cm-1 and 3200 3400 cm-1) were identified too. The spectrum further contains peaks of HCN (713cm-1) and C2H2 (729 cm-1) from which graphs of methane concentration dependence was obtained
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