The Influence of CO2 Admixtures on the Product Composition in a Nitrogen-Methane Atmospheric Glow Discharge Used as a Prebiotic Atmosphere Mimic.

This work extends our previous experimental studies of the chemistry of Titan's atmosphere by atmospheric glow discharge. The Titan's atmosphere seems to be similarly to early Earth atmospheric composition. The exploration of Titan atmosphere was initiated by the exciting results of the Cassini-Huygens mission and obtained results increased the interest about prebiotic atmospheres. Present work is devoted to the role of CO2 in the prebiotic atmosphere chemistry. Most of the laboratory studies of such atmosphere were focused on the chemistry of N2 + CH4 mixtures. The present work is devoted to the study of the oxygenated volatile species in prebiotic atmosphere, specifically CO2 reactivity. CO2 was introduced to the standard N2 + CH4 mixture at different mixing ratio up to 5 % CH4 and 3 % CO2. The reaction products were characterized by FTIR spectroscopy. This work shows that CO2 modifies the composition of the gas phase with the detection of oxygenated compounds: CO and others oxides. There is a strong influence of CO2 on increasing concentration other products as cyanide (HCN) and ammonia (NH3).

Study of nitrogen flowing afterglow with mercury vapor injection.

The reaction kinetics in nitrogen flowing afterglow with mercury vapor addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure nitrogen was created in a quartz tube at the total gas pressure of 1000 Pa and discharge power of 130 W. The mercury vapors were added into the afterglow at the distance of 30 cm behind the active discharge. The optical emission spectra were measured along the flow tube. Three nitrogen spectral systems--the first positive, the second positive, and the first negative, and after the mercury vapor addition also the mercury resonance line at 254 nm in the spectrum of the second order were identified. The measurement of the spatial dependence of mercury line intensity showed very slow decay of its intensity and the decay rate did not depend on the mercury concentration. In order to explain this behavior, a kinetic model for the reaction in afterglow was developed. This model showed that the state Hg(6 (3)P1), which is the upper state of mercury UV resonance line at 254 nm, is produced by the excitation transfer from nitrogen N2(A ³Σ(u)⁺) metastables to mercury atoms. However, the N2(A ³Σ(u)⁺) metastables are also produced by the reactions following the N atom recombination, and this limits the decay of N2(A ³Σ(u)⁺) metastable concentration and results in very slow decay of mercury resonance line intensity. It was found that N atoms are the most important particles in this late nitrogen afterglow, their volume recombination starts a chain of reactions which produce excited states of molecular nitrogen. In order to explain the decrease of N atom concentration, it was also necessary to include the surface recombination of N atoms to the model. The surface recombination was considered as a first order reaction and wall recombination probability γ = (1.35 ± 0.04) × 10(-6) was determined from the experimental data. Also sensitivity analysis was applied for the analysis of kinetic model in order to reveal the main control parameters in the model.

Study of argon flowing afterglow with nitrogen injection.

In this work, the reaction kinetics in argon flowing afterglow with nitrogen addition was studied by optical emission spectroscopy. The DC flowing post-discharge in pure argon was created in quartz tube at the total gas pressure of 1000 Pa and discharge power of 60 W. The nitrogen was added into the afterglow at the distance of 9 cm behind the active discharge. The optical emission spectra were measured along the flow tube. The argon spectral lines and after nitrogen addition also nitrogen second positive system (SPS) were identified in the spectra. The measurement of spatial dependence of SPS intensity showed a very slow decay of the intensity and the decay rate did not depend on the nitrogen concentration. In order to explain this behavior a kinetic model for reaction in afterglow was developed. This model showed that C (3)Πu state of molecular nitrogen, which is the upper state of SPS emission, is produced by excitation transfer from argon metastables to nitrogen molecules. However, the argon metastables are also produced at Ar2(+) ion recombination with electrons and this limits the decay of argon metastable concentration and it results in very slow decay of SPS intensity.

Ionic chemistry of tetravinylsilane cation (TVS+) formed by electron impact: theory and experiment.

We performed experimental and ab initio studies on tetravinylsilane cation (TVS(+)) and its ionic and neutral fragmentation products. The aim of the study is the assignment of the products formed in electron impact ionization reaction of TVS. The experimental data were compared with ab initio data calculated at the MP2/cc-pVDZ level of theory. We found good agreement between the calculated reaction enthalpies and experimental appearance energies of the ions. More generally, our calculations reveal that there is a competition between intramolecular isomerization and fragmentation processes occurring after ionization of TVS, leading to the formation of a multitude of neutral and ionic species important for characterizing the silicon-carbon-containing plasma and media. New routes for the synthesis of bearing silicon molecules are suggested.