Dr Antonin Knizek: Publications

Decomposition of Benzene during Impacts in N₂-dominated Atmospheres

The Astrophysical Journal American Astronomical Society 945:2 (2023) 149-149

Authors:

Lukáš Petera, Antonín Knížek, Vojtěch Laitl, Martin Ferus

Abstract:

Abstract Benzene is a simple neutral aromatic compound found in molecular clouds, comets, and planetary atmospheres. It has been confirmed on Jupiter, Saturn, Titan, and is expected on exoplanets. In this paper, the decomposition of benzene in a simulated asteroid or comet impact into an N2-dominated atmosphere was investigated. The impact plasma was simulated with laser-induced dielectric breakdown and the gas phase decomposition products were observed using high-resolution Fourier transform infrared spectroscopy. The gas phase decomposition products involve mainly HCN, C2H2, and smaller amounts of CH4 with yields of 3.1%–24.0%, 0–11.7%, and 0.5%–3.3%, respectively. Furthermore, in presence of water, benzene also produces CO and CO2 with yields of 2.4%–35.1% and 0.01%–4.8%, respectively. The oxidation state of the product mixture is proportional to the water content. Apart from that, a black-brownish solid phase is formed during the experiments, which makes up about 60% of the original carbon content. Our results therefore show that in anoxic N2-dominated planetary atmospheres, impacts might lead to the depletion of benzene and the formation of HCN, C2H2, and CH4 and, in the presence of water, to the formation of CO and CO2.

Origin of Methane and Biomolecules from a CO2 Cycle on Terrestrial Planets

Springer International Publishing (2023) 329-335

Authors:

Svatopluk Civiš, Antonín Knížek, Martin Ferus

 Impact-induced transformation of simple aromatic compounds in planetary atmospheres

(2022)

Authors:

Lukáš Petera, Antonín Knížek

Abstract:

<div>Asteroids and comets are often rich in polyaromatic hydrocarbons (PAHs), which represent in general about 30 % of total carbon in space. The fate of these molecules in extraterrestrial delivery was investigated by experimentally simulating asteroid impacts &#8211; using laser induced breakdown (LIBD) &#8211; into rocky planetary atmospheres and surfaces. Experiments were performed with benzene, naphtalene and anthracene as simple members of PAHs. The effect of LIBD on chemistry of these compounds in various chemical environments, such as atmospheric composition and solid phase matrices, were also studied. The main gas phase products are acetylene and HCN, followed by CO and CO2, whose yields mainly depend on the content of water vapour in the atmosphere. A brownish solid product was also observed. Therefore, simple aromatic compounds, and likely also PAHs, can be a viable source of HCN &#8211; molecule with significant prebiotic importance&#8211; in planetary environments.</div> <div>&#160;</div>

Abiotic chemical routes towards the phosphine synthesis in the atmosphere of Venus

(2022)

Authors:

Martin Ferus, Giuseppe Cassone, Paul Rimmer, Franz Saija, Klaudia Mráziková, Antonín Knížek, Svatopluk Civiš

Abstract:

<p>Several of the Venera, Vega and Pioneer probe data as well as ground based observation support the presence of so-called Redox Disequilibrium Pairs (RDPs) in atmosphere of so hostile world as Venus (Greaves 2021). State of the art chemical networks cannot explain origin of an important RDP, phosphine, in oxidized atmosphere of Venus by a conventional processes (Bains 2021). We used the hybrid Density Functional Theory (DFT) for investigation of a series of chemical reaction pathways leading to the reduction of phosphate monoxide to phosphine. Our calculations indicated that a reaction network similar to photochemical synthesis of methane from carbon monoxide over acidic surfaces suggested for Mars (Civi&#353; 2019) can also occur in clouds of Venus. As a seminal step, we have explored &#8211; via state-of-the-art quantum-based calculations &#8211; the a priori energetic feasibility of the following reaction:</p><p>HCO(radical) + PO = CO2 + PH (biradical).</p><p>Our calculations have shown that chemical conversion is constituted of three steps. Two of them are energetically favoured, however, the final conversion to phosphine is hardened by a significant activation barrier. This barrier can be overcome by a reaction of OPH radical with hydrogen radical. For assessing the potential of the newly introduced reaction mechanisms, models of the Venus and early Earth atmospheres in ARGO code and modified STAND chemical network were created and verified. Comparison of reaction yields suggests that this pathway is potentially effective enough and could be the source of phosphine recently discovered on Venus.&#160;</p><p>We acknowledge the support provided by the Czech Science Foundation within the project reg. no. 21-11366S and by ERDF/ESF "Centre of Advanced Applied Sciences" (No. CZ.02.1.01/0.0/0.0/16_019/0000778). We acknowledge support of the Czech Academy of Sciences, Strategy AV21, project VP16. The Czech team is part of the VenSpec-H Consortium onboard the ESA EnVision mission.</p><p>References:</p><p>Civi&#353; S. et al.: Formation of Methane and (Per)Chlorates on Mars. ACS Earth Space Chem. 2019, 3, 2, 221&#8211;232.</p><p>Bains W. et al.: Phosphine on Venus Cannot Be Explained by Conventional Processes. Astrobiology 2021, 10 (21), 1277-1304.</p><p>Greaves J. S. et al.: &#160;Phosphine gas in the cloud decks of Venus. Nature Astronomy 2021, 5, 655&#8211;664.</p>

The stability of benzene in planetary atmospheres

(2022)

Authors:

Antonín Knížek, Lukáš Petera

Abstract:

<p>Benzene is the simplest organic compound with a 6-carbon aromatic ring. As such, it was used as a first order representative of aromatic compounds in planetary atmospheres. These compounds can be brought by asteroid&#160;impacts into rocky planetary atmospheres, where they can serve as precursors for further synthesis. Our experiments show that benzene vapours in nitrogen-dominated atmospheres subjected to asteroid&#160;impacts (modelled by laboratory laser shots) lead&#160;to the formation of acetylene and hydrogen cyanide. Both these products appear in many proposed mechanisms of prebiotic chemistry.</p>

51��