This diploma thesis deals with the study of plasmachemical processes and the synthesis of chemical compounds in gas mixtures simulating prebiotic atmospheres, with a primary focus on the conditions prevailing on the moon Titan and the planet Mars. A glow discharge at atmospheric pressure was used as an energy source to initiate the chemical reactions. The work investigates the influence of the gas mixture composition, particularly the addition of methane and oxygen to the nitrogen carrier gas, on the physical character of the discharge and the synthesized products.
In situ plasma diagnostics were performed using optical emission spectrometry (OES). The first negative systém of nitrogen, second positive system of nitrogen, the violet system of the CN radical, and the Swan system of the C_2 molecule were identified in the measured spectra. Furthermore, hydrogen Balmer lines (H_α, H_β) were also detected. These spectra were subsequently utilized to calculate the rotational and vibrational temperatures of the plasma. A strong dependence of the emission of these species on the varying methane flow rate was observed. At higher methane flow rates, energy depletion of the discharge and chemical oversaturation occurred, leading to the preferential formation of more complex structures. Conversely, in the oxidative regime (O_2 addition), a significant decrease in the monitored radicals was demonstrated as a result of the highly effective oxidation of carbon and hydrogen fragments.
Proton transfer reaction time-of-flight mass spectrometry (PTR-TOF-MS) was utilized for the identification and analysis of the resulting stable gaseous products. In the reductive regime, this method confirmed the formation of nitriles and hydrocarbons. The primary compounds detected in this environment included ammonia, acetylene, hydrogen cyanide, acetonitrile, and benzene. Upon transition to the oxidative regime, a decline in the synthesis of nitriles was demonstrated, as they were effectively replaced by oxygenated compounds. The production of the prebiotically key formamide and acetaldehyde became dominant, accompanied by other compounds such as simple alcohols and carboxylic acids.
The results of this thesis provide valuable insights into the kinetics of plasmachemical reactions and demonstrate the fundamental differences between reductive and oxidative conditions during the transformation of simple precursors into more complex molecules. This contributes to a better understanding of chemical evolution in planetary atmospheres.
Although the presented work yields numerous valuable findings, it simultaneously opens up a broad scope for subsequent research. The experiments conducted thus far were performed at laboratory temperature, which fundamentally differs from the extreme conditions on the surface of Titan (approximately −180 °C) or Mars (average −63 °C). Given that temperature critically influences the kinetics of recombination processes, an even more pronounced synthesis of complex organic macromolecules can be anticipated under cryogenic conditions. These substances may represent key prebiotic precursors, the study of which is essential for a deeper understanding of chemical evolution and for elucidating the mechanisms that could have led to the emergence of life on early Earth.