EXOA3
Either the hypothesis that the supply of organic molecules necessary for the emergence of life is of extraterrestrial origin or the hypothesis that such organic molecules were synthesized locally on Earth as it is done in other planets or moons of our Solar System (or beyond) require convincing evidence that only space exploration in search of molecular complexity can provide. In this symposium, we will analyze the state of the art of our knowledge on the degree of complexity that organic molecules can reach in the interstellar medium (with particular attention to star-forming regions and protoplanetary disks), in comets, asteroids, meteorites, and interplanetary dust particles as well as in the planets and moons of the Solar System. Contributions on the detection of organic molecules in space, on laboratory experiments to determine their formation pathways, on astrochemical or photochemical models as well as on implications in astrobiology are welcome.
Our is the only planet known with such complex chemistry that give rise to life. Numerous evidence suggests that molecular complexity had already begun and developed when the Solar System was an embryo inside a cold molecular cloud. In this presentation, I will present the major advances in our comprehension of chemistry during those ancient eons, based on what we observe in the young solar-like planetary systems forming in the Sun’s vicinity today and our ability to understand them. I will also give an overview of the many challenges that remain to be overcome.
How to cite: Ceccarelli, C.: Molecular Complexity in forming Solar-like Planetary Systems , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-839, 2024.
Complex organic molecules are detected in the gaseous and solid phases of molecular clouds and protoplanetary disk. The origin of these molecules is still debated, but a large part is supposed to form on the surface of frozen grains. These icy grains, observable in dense molecular clouds, will be altered by highly energetic processes (VUV photons, ions, electrons) during the formation of planetary systems. These alterations allow the activation of molecules initially present in these ices, resulting in the development of a significant chemical reactivity. In certain environments such as the solar nebula, these grains can be heated, releasing in the gas phase a large part of the complex organic molecules initially formed on the surface or within the ice bulk. Some of these molecules can also react inside the ice forming nonvolatile molecules that remain on the grains leading to the formation of refractory organic residues. Part of the transformed grains can then agglomerate, resulting in interplanetary objects such as comets or asteroids. As a result, some of the organic matter present in solar system objects could come be inherited from ices found in dense molecular clouds.
On the basis of laboratory experiments, we develop an analytical strategy to study the chemistry generated by the processing of such ices during simulated solar system formation. We particularly demonstrated the richness of molecules formed in refractory organic residues [1]. We also investigated the composition of the gas phase depending of the initial composition of the ice [2] as well as the molecular composition of the refractory organic residues [3,4]. Finally, we demonstrated how this matter can evolve inside asteroids, parent bodies of meteorites in our solar system [5].
All results obtained from these experiments suggest that ices of astrophysical objects are key environments to generate a rich molecular diversity, as it could be for our solar system, and question the role of this exogenous reservoir in the emergence of life on Earth.
[1] G. Danger, F-R. Orthous-Daunay, P. de Marcellus, P. Modica, V. Vuitton, F. Duvernay, L. Le Sergeant d’Hendecourt, R. Thissen, and T. Chiavassa, Geochimica & Cosmochimica Acta, 2013, 118, 184
[2] N. Abou Mrad, F. Duvernay, R. Isnard, T. Chiavassa and G. Danger. The Astrophysical Journal, 2017, 846, 124
[3] A. Fresneau, N. Abou Mrad, L. LS d’Hendecourt, F. Duvernay, L. Flandinet, F-R Orthous-Daunay, V. Vuitton, R. Thissen, T. Chiavassa, G. Danger. The Astrophysical Journal, 2017, 837, 168
[4] G. Danger, A. Ruf, T. Javelle, J. Maillard, V. Vinogradoff, C. Afonso, I. Schmitz-Afonso, L. Remusat, Z. Gabelica and P. Schmitt-Kopplin, Astronmy and Astrophysics, 2022, DOI: 10.1051/0004-6361/202244191
[5] G. Danger, V. Vinogradoff, M. Matzka, J-C. Viennet, L. Remusat, S. Bernard, A. Ruf, L. Le Sergeant d’Hendecourt and P. Schmitt-Kopplin. Nature Communication, 2021, 12, 3538
How to cite: Danger, G., Honold, L., Ruf, A., Javelle, T., Garcia, A., Schmitt-Kopplin, P., and Vinogradoff, V.: Ices as a source of molecular diversity in astrophysical environments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-596, 2024.
Polycyclic aromatic hydrocarbons (PAHs) are widely observed in space both in the gas phase and as components of interstellar dust. PAHs account for ~20% of the carbon (C) in space. Understanding the mechanism to unlock C from PAHs is important to shed light on the formation of complex organic molecules (COMs), which play a crucial role in regulating the physics and chemistry of our universe and aiding in the origin of life [1]. While COM formation often begins with CO activation via hydrogenation on the surface of interstellar grains, the breakdown of gas-phase PAHs could provide an alternative pathway. PAHs often host radicals such as oxygen (O) and hydrogen (H), which weaken their aromatic bonds. While superhydrogenation of PAHs is well-studied [2], their interaction with atomic O as a possible route for their fragmentation remains underexplored [3].
Using density functional theory (DFT) and instanton theory [4], we predicted intermediate formations resulting from the reaction of O with naphthalene in the gas phase (Figure 1) and computed accurate tunneling rates. Similar to PAH hydrogenation, DFT suggests a sequence of O attachment. Once atomic oxygen reacts with the first C atom of naphthalene, intersystem crossing occurs from the triplet to the singlet spin state. O initially bridges Cs in naphthalene, catalyzing the barrier-less breakdown of a C-C bond, thus forming a heterocyclic ring. Subsequent oxygenation breaks down the PAH structure. Computed instanton rates reveal that tunneling is dominant at temperatures below 50K, with both O and C atoms tunneling through the potential barrier, aiding in the opening of the aromatic ring. Once one of the PAH rings is opened, the attack of two H leads to the fragmentation of the PAH, forming formaldehyde. These findings may clarify the role of PAHs in the formation of COMs, potentially linking them to the organic inventory formation in star-forming regions [1].
Figure 1: Oxygenation (in red) and hydrogenation (in black) tunneling of naphthalene aiding in fragmentation in the gas phase.
References
[1] Tielens, A. G. G. M. Rev. Mod. Phys. 2013, 85, 1021.
[2] Campisi, D.; et al. Phys. Chem. Chem. Phys. 2020, 22, 1557-1565.
[3] Cavallotti, C.; et. al. J. Phys. Chem. Lett. 2020, 11, 22, 9621–9628.
[4] Rommel, J. B.; et. al. J. Chem. Theory Comput. 2011, 7, 3, 690–698.
How to cite: Campisi, D.: Tunneling Toward Interstellar PAHs: O and H’s Quantum Leap , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-887, 2024.
The presence of molecules in the extreme physical conditions of the interstellar medium (ISM) was considered impossible, until in 1937 the first diatomic species were observed. Since then, about 300 gaseous species were identified and, in the coldest environments, the presence of dust grains made of silicates and carbonaceous material covered in water-dominated ice mantles was discovered1,2. Ethanol (CH3CH2OH) is a relatively common molecule, often found in star-forming regions. Recent studies suggest that it could be a parent molecule of several so-called interstellar complex organic molecules (iCOMs), that are the building blocks of the molecules responsible for the origin of life, and are thought to be inherited through the different stages of the evolution of a planetary system3. Similarly, urea (NH2CONH2) is thought to be the precursor of purines and pirimidines. It has been detected in few sources of the ISM and in Murchison meteorite, with the unique characteristic of possessing two C–N bonds. Being stable against ultraviolet radiation and high-energy electron bombardment, urea is expected to be present in interstellar ices4.
However, the formation route of these species remains under debate. In the present work, we investigated the formation of ethanol and urea on the surface of the icy mantles coating dust grains in the ISM with quantum chemical simulations. Two clusters of 18 and 33 water molecules were adopted as ice models and DFT calculations were run with Gaussian and ORCA codes.
The “radical + ice component” scheme was tested as an alternative mechanism for the synthesis of ethanol, beyond the usual radical−radical coupling5,6. Results indicate that CH3CH2OH can potentially be formed by this proposed reaction mechanism. The reaction of CCH with an H2O belonging to the water ice clusters can be barrierless, leading to the formation of vinyl alcohol precursors (H2CCOH and CHCHOH). Subsequent hydrogenation of vinyl alcohol yielding ethanol is the only step presenting a low activation energy barrier. In this case, the positive outcome of the “radical + ice component” scheme is due to the establishment of a hemibond interaction between the two reactants.7
Theoretical and experimental studies suggest that isocyanic acid (HNCO) and formamide (NH2CHO) are possible precursors of urea.8 Here, the application of the same “radical + ice component” scheme to the synthesis of urea was not straightforward, as HNCO and NH2CHO (or, alternatively, NH3) are less abundant then water on the icy mantles.9 Alternatively, different mechanisms involving both closed-shell and open-shell species were investigated, and the radical–radical NH2CO + NH2 coupling was found to be the most favourable pathway due to being almost barrierless and more favoured than the competitive H-abstraction reaction returning NH3 +HNCO. In this path, the presence of the icy surfaces is crucial for acting as reactant concentrators/suppliers, as well as third bodies able to dissipate the energy liberated during the urea formation.10
References
[1] B.A. McGuire, Astrophys. J. Supplem. S. 259(30), 154104 (2022)
[2] A.A. Boogert, P.A. Gerakines, D.C. Whittet, Annu. Rev. Astron. Astr. 53, 541-581 (2015)
[3] P. Caselli, C. Ceccarelli, Astron. Astrophys. Rev. 20, 56 (2012)
[4] V.J. Herrero, I. Tanarro, I. Jiménez-Serra, H. Carrascosa, G.M. Muñoz Caro, B. Maté, Mon. Not. R. Astron. Soc. 517, 1058–1070 (2022)
[5] J. Enrique-Romero, A. Rimola, C. Ceccarelli, P. Ugliengo, N. Balucani, D. Skouteris, ACS Earth Space Chem. 3, 2158-2170 (2019)
[6] A. Rimola, D. Skouteris, N. Balucani, C. Ceccarelli, J. Enrique-Romero, V. Taquet, P. Ugliengo, ACS Earth Space Chem. 2, 720-734 (2018)
[7] J. Perrero, J. Enrique-Romero, B. Martínez-Bachs, C. Ceccarelli, N. Balucani, P. Ugliengo, A. Rimola, ACS Earth Space Chem. 6, 496−511 (2022)
[8] E.C.S. Slate, R. Barker, R.T. Euesden, M.R. Revels, A.J.H.M. Meijer, Mon. Not. R. Astron. Soc. 497, 5413-5420 (2020)
[9] M.K. McClure, W. Rocha, K. Pontoppidan, N. Crouzet, L.E. Chu, E. Dartois, T. Lamberts, J. Noble, Y. Pendleton, G. Perotti, et al., Nat. Astron. 7, 431-443 (2023)
[10] J. Perrero, A. Rimola, Icarus, 410, 115848 (2024)
How to cite: Perrero, J., Ugliengo, P., and Rimola, A.: Formation of Complex Organic Molecules on dust grains surfaces: a Quantum Mechanical approach, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-89, 2024.
The preference for l-amino acids in proteins and d-sugars in nucleic acids is a key feature of life. The origin and evolution of biological homochirality still remains unresolved. Abiotic l-enrichments of amino acids in carbonaceous chondrites provide a strong hint that life’s homochirality originated beyond Earth.1 This, however, hinders the identification of chiral biosignatures of putative past life in current and future space missions. Would a detection of a set of enantioenriched amino acids on Mars, for example, point to traces of extinct life blurred by years of racemisation, or would it merely be a product of abiotic physico-chemistry operating in harsh extra-terrestrial environments? Understanding the origin of small chiral imbalances in solar system bodies and the amplification to life’s homochirality will aid in answering these questions. To date, stellar ultraviolet circularly polarized light (UV CPL) has been recognized as one of the promising candidates for triggering symmetry breaking in interstellar environments.2 Monochromatic UV CPL has proven capable of inducing enantiomeric excesses in amino acids via asymmetric photolysis,3-5 as predicted by their anisotropy spectra. While these are important proof of concept experiments to validate the astrophysical CPL scenario, comparisons of the net effect of broadband CPL with the results of enantioselective analyses of extra-terrestrial samples are necessary. I will outline how a strategic selection of analytes can provide useful insights into the CPL scenario and the origins of chiral biases in extra-terrestrial samples. Here, our latest results on isovaline will be presented,6 which ultimately provide a sound explanation for its varying enantiomeric excesses detected in carbonaceous chondrites that have been extensively discussed in the origin-of-life research community over the last two decades. Given their relatively high recalcitrance and resistance to degradation, lipids are one of the best candidate biomarkers in exobiology.7 Our recently recorded anisotropy spectra of membrane lipids and their chiral backbones8 provide guidelines for future enantioselective analyses of interstellar ice analogues, meteorites and return samples, in particular from Hayabusa2 and OSIRIS-REx missions, the Mars Sample Return Campaign, as well as for the search for traces of life in space by the ExoMars 2028 and Martian Moons eXploration missions.
[1] Glavin, D. P.; Burton, A. S.; Elsila, J. E.; Aponte, J. C.; Dworkin, J. P. Chem. Rev. 2020, 120, 4660.
[2] Garcia, A. D.; Meinert, C.; Sugahara, H.; Jones, N. C.; Hoffmann, S. V.; Meierhenrich, U. J. Life 2019 9, 29.
[3] Flores, J. J.; Bonner, W. A.; Massey, G. A. J. Am. Chem. Soc. 1977, 99, 3622.
[4] Meinert, C.; Hoffmann, S. V.; Cassam-Chenaï, P.; Evans, A. C.; Giri, C.; Nahon, L.; Meierhenrich, U. J. Angew. Chem. Int. Ed. 2014, 53, 210.
[5] Modica, P.; Meinert, C.; de Marcellus, P.; Nahon, L.; Meierhenrich, U. J.; d'Hendecourt, L. L. S. Astrophys. J. 2014, 788, 79.
[6] Bocková, J.; Jones, N. C.; Topin, J.; Hoffmann, S. V.; Meinert. C. Nat. Commun. 2023, 14, 3381.
[7] Bocková, J.; Jones, N. C.; Hoffmann, S. V.; Meinert. C. Nat. Rev. Chem. 2024, accepted.
[8] Bocková, J.; Garcia A. D.; Jones, N. C.; Hoffmann, S. V.; Meinert. C. Chirality 2024, 36, e23654.
Acknowledgement
Supported by the European Research Council under the European Union’s Horizon 2020 research and innovation programme [grant agreement 804144].
How to cite: Bocková, J., D. Garcia, A., Topin, J., C. Jones, N., V. Hoffmann, S., and Meinert, C.: Deciphering the origins of life’s asymmetry: The search for biosignatures in space, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-634, 2024.
The presence of dimethyl sulfide (DMS) in the atmosphere of exoplanets has been invoked as a potential biosignature since its presence atmosphere of Earth has a biological origin. Dimethylsulfoniopropionate (DMSP) is produced by phytoplankton and then degraded to form methanethiol (CH3SH) and DMS. Microbial methylation and detoxification processes can also produce DMS from hydrogen sulfide H2S.
Recently, a tentative detection of DMS on the candidate Hycean exoplanet K2-18 b was reported in the work by Madhusudhan et al. [1]. Dimethyl sulfide is also detected in the coma of comet 67P/Churyumov-Gerasimenko [2], and its isomers ethyl mercaptan, CH3CH2SH, has been detected toward Orion KL [3]. Therefore, DMS adds to the list of S-bearing molecules identified at the moment in the extraterrestrial environment.
No formation routes of extraterrestrial DMS are reported in the literature at the moment. Therefore, we have started a systematic theoretical investigation to unveil the possible formation mechanisms of DMS in the gas phase. We make use of electronic structure calculations of the relevant potential energy surfaces and kinetics calculations to derive the energy profile and rate coefficients of each proposed reaction following the same schemes that we have previously identified for the formation of the analogous O-bearing species dimethyl ether [4].
[1] Madhusudhan, Nikku, et al. "Carbon-bearing molecules in a possible hycean atmosphere." The Astrophysical Journal Letters 956.1 (2023): L13.
[2] Hänni, N., et al. "Identification and characterization of a new ensemble of cometary organic molecules." Nature Communications 13.1 (2022): 3639.
[3] Kolesniková, Lucie, et al. "Spectroscopic characterization and detection of ethyl mercaptan in orion." The Astrophysical Journal Letters 784.1 (2014): L7.
[4] Skouteris, Dimitrios, et al. "Interstellar dimethyl ether gas-phase formation: a quantum chemistry and kinetics study." Monthly Notices of the Royal Astronomical Society 482.3 (2019): 3567-3575.
How to cite: Di Genova, G., Giustini, A., Mancini, L., Rosi, M., Ceccarelli, C., and Balucani, N.: Possible gas-phase formation routes of dimethyl sulfide in extraterrestrial environments, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-435, 2024.
The process that led to the formation of our Solar System and the origin of the observed prebiotic compounds are among the most exciting open questions in modern astrochemistry. The first results of the Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars (FAUST; PI: S. Yamamoto; Codella et al. 2021) ALMA Large Program suggest that the chemical composition and fate of future planetary systems strongly depend on the history of the parental protostellar envelope.
I will present new FAUST high-angular resolution (50 au) observations of interstellar Complex Organic Molecules (iCOMs; i.e. organic molecules with at least 6 atoms; Ceccarelli et al. 2017) and dust continuum emission towards the Corona Australis (CrA) star cluster (see Figure 1). The CH₃OH emission reveals an arc-structure at ~1800 au from the protostellar system IRS7B along the direction perpendicular to the disk major axis (see Figure 2a). The arc is located at the edge of two elongated continuum structures that define a cone emerging from IRS7B (see Figure 1). The region inside the cone is probed by H ₂ CO (see Figure 2d), while the eastern wall of the arc shows bright emission in SiO, a typical shock tracer (see Figure 2e). Taking into account the association with a previously discovered radio jet imaged with JVLA at 6 cm, the molecular arc reveals for the first time a bow shock driven by IRS7B and a two-sided dust cavity opened by the mass-loss process.
We derive for each cavity wall an average H2 column density of ∼ 7×1021 cm-2 , a mass of ∼ 9×10-3 M⊙ , and a lower limit on the dust spectral index of 1.4.
These observations provide the first evidence of the shock and the conical dust cavity opened by the jet driven by IRS7B, with important implications for the chemical enrichment and grain growth in the envelope of Solar-System analogues.
Figure 1: Left: SCUBA map at 450µm; Central: ALMA map of 1.3mm continuum emission from Sabatini et al (2024). Right: Zoom around IRS7B. Our ALMA continuum map reveals for the first time the dust grains in the walls of the cavity (cyan dashed lines) opened by the jet driven by IRS7B (cyan solid line).
Figure 2: Moment 0 of (a) CH3OH-E (42,3 -31,2), (b) CH3OH-A (51,4-41,3), (d) p-H2CO (30,3-20,2), (e) SiO (5-4) lines, around the molecular arc (integrated from 0 to +12 km s−1). Cyan lines and arrows follow Figure 1. The white contours mark the 5σ emission. Small circles indicate the positions of the brightest spots in CH3OH (42,3-31,2), SiO (5-4), and p-H2CO (30,3-20,2), i.e. labelled “A”, “B” and “C”, respectively. Red cross indicates the position of SMM 1A (Figure 1). The green semicircle shows the ALMA Band 6 FoV, while the grey background delimits the region inside each ALMA pointing.
How to cite: Sabatini, G., Podio, L., Codella, C., Ceccarelli, C., Chandler, C. J., Sakai, N., and Yamamoto, S.: Dusty cavity and molecular shock driven by IRS7B in the CoronaAustralis Cluster, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1108, 2024.
The reactivity of atomic nitrogen in its ground state (4S) with closed shell molecules, like hydrocarbons, is very low, while atomic nitrogen in its first electronically excited 2D state shows a significant reactivity with hydrocarbons. N(2D) was detected in the water-poor comet C/2016 R2 (Pan-STARRS)(Raghuram et al. 2020) and in a plethora of strongly photon-irradiated environments including the Orion Nebula (M42), low-ionization H II regions (M43), planetary nebulae (i.e. the Ring Nebula), supernova remnants (i.e. the Crab Nebula), and Herbig-Haro objects (Ferland et al. 2012, Dopita et al. 1976, Ferland et al. 1988, Bautista 1999).Polycyclic aromatic hydrocarbons (PAHs) and related species are presumed to be omnipresent in the interstellar medium (ISM) and aromatic chemistry is widespread in the earliest stages of star formation.
Nitrogen, in its molecular form, and hydrocarbons, both aliphatic and aromatic, are also the main components of the atmosphere of Titan (Hörst 2017, Vuitton et al. 2006). This atmosphere is similar, in some aspects, to the primordial atmosphere of Earth (Vuitton et al. 2013, Balucani 2012) and for this reason has been extensively studied by several missions (Brown et al. 2010), Lai et al. 2017). Among the hydrocarbons identified on Titan there is benzene (Vuitton et al. 2008, Clark et al. 2010), while toluene is easily produced by the reaction of C6H5, obtained by photodissociation of benzene, and CH3 (Loison et al. 2019). Dinitrogen in the atmosphere of Titan can dissociate into atomic nitrogen both in its ground state or 2D excited state in similar amounts (Lavvas et al. 2011, Dutuit et al. 2013) and N (2D) can easily react with other constituents of the upper atmosphere of Titan or with species present in the ISM medium (Balucani 2013, Balucani 2009, Imanaka & Smith 2010, Balucani et al. 2001, Balucani et al. 2006, Homayoon et al. 2014, Balucani et al. 2015, Israel et al. 2005).
In this contribution, we report on a theoretical characterization of the reaction involving N(2D) and simple aromatic hydrocarbons, like benzene (Balucani et al. 2018, 2019, 2023), toluene (Rosi et al. 2020. 2021) or pyridine (Mancini et al. 2024). We have already investigated the reactions of atomic nitrogen in its excited 2D state with various aliphatic hydrocarbons, like CH4 (Balucani et al. 2009), C2H2 (Balucani et al. 2000A), C2H4 (Balucani et al. 2000B, 2012), C2H6 (Balucani et al. 2010), allene (Vanuzzo et al. 2022), methylacetylene (Mancini et al. 2021), alkynes (Mancini et al. 2020) in laboratory experiments by the crossed molecular beam technique with mass spectrometric detection and time-of-flight analysis at different collision energies complemented by electronic structure calculations of the stationary points along the minimum energy path and kinetics calculations. The aim is to determine the chemical behavior of N(2D) with aromatic species after the previous investigation with aliphatic molecules. In particular, we wish to establish whether the aromatic ring is preserved in this reaction and whether the N atom is incorporated in the ring of carbon atoms.
References
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Balucani N. Int. J. Mol. Sci., 10 2304 (2009)
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Balucani N. et al. Faraday Discussions 147 189 (2010)
Balucani N. et al. J. Phys. Chem. A 116 10467 (2012)
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Balucani N. et al. LNCS 10961 763 (2018)
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Brown R., Lebreton, J. P., Waite, J. (eds.): Titan from Cassini-Huygens. Springer, Netherlands (2010)
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How to cite: Rosi, M., Balucani, N., Caracciolo, A., Casavecchia, P., Faginas-Lagoi, N., Mancini, L., Skouteris, D., and Vanuzzo, G.: A joint computational and experimental study of the reactions between N(2D) and simple aromatic hydrocarbons , Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1013, 2024.
Over the last decade, there has been an important advance in the comprehension of the formation and destruction routes of the most common interstellar chemical species. However, a significant lack of knowledge concerning the chemistry of other minor species is still present, often due to the limited amount of computational and experimental data. In this contribution, the possible role of the electronically-excited sulphur S(1D) and oxygen O(1D) in the chemistry of interstellar or cometary ice has been explored through a theoretical characterization of the S(1D) reaction with H2O and CH3OH, and the O(1D) reaction with CH3SH, in the gas-phase and in the presence of a cluster of four water molecules. All the stationary points of the investigated potential energy surface (PES) were optimized at the density functional (DFT) level of theory, using the B3LYP functional and the correlation-consistent valence-polarized basis set aug-cc-pVTZ basis set, augmented with a tight d function on sulphur atoms. The presence of the 4-water-molecules cluster drastically changes the reaction mechanisms since the SO + H2 channel, which is the only open channel in the gas-phase S(1D) + H2O reaction, cannot occur due to the hindrance caused by the H-bonds between the involved reaction intermediates and the water molecules of the cluster. As regards the S(1D) + CH3OH and O(1D) + CH3SH, the only H-displacement channels together with SH- and OH-group ejection were found to be occurring, while all the other dissociation routes, which are thermally and kinetically active in the gas phase, were found to be hindered due to the presence of the water cluster. In addition, a global reduction of the energy content with respect to the reactants makes most of the H-displacement channels allowed from a thermodynamic standpoint, whereas in some cases they are endothermic, thus unfavored, for the isolated system. Overall, the ice matrix has been predicted to stabilize the reactive intermediates HSOH, H2SO, and CH2OHSH. Therefore, we started to investigate the effect of adding more water molecules by including an 18-water-molecule cluster in the case of the S(1D) + H2O system finding an enzyme-like effect of the cluster. In fact, the reaction pathways are found to be consistently favored because of the substantial reduction of the energy barriers connecting the minima of the potential energy surface. Additional work is necessary to simulate the ice environment better and confirm these preliminary results.
Figure 1 illustrates PES arising from the S(1D) + H2O reaction in the gas phase. The bold lines of Figure 1 highlight the exothermic pathway leading to the single set of reaction products SO + H2.
Figure 2 illustrates the PES calculated at the same level of theory arising from the S(1D) + H2O reaction considering a 4-membered cluster of H2O interacting
with the reaction intermediates, reactants, and products.
Figure 2 illustrates the PES calculated at the wB97XD functional level arising from the S(1D) + H2O reaction considering a 18-membered cluster of H2O interacting with the reaction intermediates, evidencing the decrease of the minimum energy path between each intermediate of the reaction.
How to cite: Giustini, A., Balucani, N., Rosi, M., and Di Genova, G.: Theoretical investigation on reactions involving electronically-excited atoms occurring in the gas phase of extraterrestrial environments and at the surface of interstellar icy grains, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-765, 2024.
Silicon is one of the most abundant elements in the universe, and it is predominantly stored in the cores of dust grains, meteoroids, and meteorites in the form of silicates and carbides. When intense shocks occur, besides being released in the interstellar medium (ISM) as gaseous SiO and its isotopologues, silicon can be set free in its elemental form, ready to further react [e.g., 1, 2]. Relevant to this study, SiS has been detected in few astronomical environments: the interstellar shocked regions of L1157-B1, associated with an outflow driven by a low-mass protostar, and of the massive star-forming regions Sgr B2, and Orion KL, in addition to the envelopes of C-rich evolved stars [e.g., 3, 4]. Whilst the aspects related to the formation and destruction of SiO have been deeply investigated, those regarding SiS have not been clarified yet. The current available databases involving molecular kinetics (e.g. KIDA1, UMIST2), indeed report a single reaction pathway representing the SiS formation (HSiS+ + e- → H + SiS), leaving a plethora of potential channels to be investigated. Regarding the formation of SiS starting from Si+ via the HSiS+/SiSH+ ionic channel, many aspects are not fully clarified, and existing data in the literature is uncertain or missing. SiSH+ could be formed starting from Si+ through the reaction with OCS (to give SiS+ + CO) and subsequently with H2. However, the SiS+ + H2 → H + SiSH+ reaction seems unlikely [5]. H2S, which is detected also in shocked regions along with SiS [6], could also react with Si+ leading to HSiS+/SiSH+. Such a reaction pathway is not reported in KIDA or UMIST databases, despite H2S is expected to be released from the grains in the shocked regions where also SiS is detected. The formation of SiS from HSiS+/SiSH+ occurs through a proton transfer reaction towards an acceptor (e.g. NH3). In the present work, we aim to investigate the chemistry behind the Si+ + H2S reaction as a relevant ionic pathway to the formation of SiS and to generate new information available for the current reaction networks. To do so, we report both experimental and theoretical results, i.e. the rate constant, the absolute reactive cross section, and the branching ratios for the investigated ion-molecule reaction. The experiments were performed by using a Guide Ion Beam Mass Spectrometer (GIB-MS) with an O1-Q1-O2-Q2 configuration. The ions are generated in the source by electron impact ionization and then cooled and guided through the first octupole (O1) and quadrupole (Q1) to the collision cell, a second octopole (O2), where the neutral gas is injected and the reaction occurs. The products are then mass-filtered through the second quadrupole (Q2) and finally detected. The observables retrieved from this experiment are the branching ratios for the several reaction channels, the absolute reactive cross section for the investigated chemical reaction, and its trend as a function of the collision energy. The theoretical investigation was carried out combining high level ab initio calculations and statistical analysis. In details, electronic structure calculations on the doublet potential energy surface (PES) were performed at the coupled-cluster (CCSD(T)) level of theory, for both geometry optimization and harmonic vibrational frequencies calculations. On the basis of the derived PES, a kinetic investigation was performed adopting a combination of Capture theory and Rice-Ramsperger-Kassel-Marcus (RRKM) theory, in order to derive branching fractions and channel specific rate constants. For the Si+ + H2S system, the observed reaction channels were the formation of SiSH+ + H and SiS+ + H2. The SiSH+ formation channel is observed to be the main one, in agreement with the theoretical results. Between the two possible SiSH+/HSiS+isomers, SiSH+ is the only one expected to form due to the endothermicity of the channel bringing to HSiS+.
References
[1] Bachiller, R. et al. (1998), “A molecular jet from SSV13B near HH7-11”, A&A 339, L49
[2] Codella, C. et al. (1999), “Low and high velocity SiO emission around young stellar objects” A&A, vol. 343, p. 585
[3] Podio, L. et al. (2017), “Silicon-bearing molecules in the shock L1157-B1: first detection of SiS around a Sun-like protostar” Mon. Not. R. Astron. Soc. Lett., vol. 470, no. 1, pp. L16–L20
[4] Zyuris. (1988), “SiS in Orion-KL: Evidence for outflow chemistry”, Astrophys. J., vol. 324, p. 544
[5] Wlodek, S. et al. (1989) “Gas-phase oxidation and sulphidation of Si+(2P), SiO+ and SiS+” J. Chem. Soc., Faraday Trans. 2, vol. 85, no. 10, pp. 1643–1654
[6] Codella C. et al. (2003) “Shocked gas around CepA: evidence from multiple outflows from H2S and SO2 observations”, M.N.R.A.S, 341 707
[7] Accolla, M. et al. (2021), “Silicon and Hydrogen Chemistry under Laboratory Conditions Mimicking the Atmosphere of Evolved Stars,” Astrophys. J., vol. 906, no. 1, p. 44
1 https://kida.astrochem-tools.org
2 https://umistdatabase.uk/database
How to cite: Michielan, M., Mancini, L., Ascenzi, D., Pirani, F., Di Genova, G., Balucani, N., Rosi, M., and Ceccarelli, C.: Unveiling the Si+ chemistry in the Interstellar Medium: an ionic reaction pathway to SiS, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-1035, 2024.
Oxygen atoms are important players in regulating the chemical complexity of the Universe. In particular, the dual ability of atomic oxygen (AO) to increase or decrease the complexity of a system is evident in the reactions between O(3P) and unsaturated aliphatic/aromatic hydrocarbons. These reactions can lead to both the formation of more complex oxygenated organic compounds and the degradation of the organics, with the formation of CO or CO2.
This last aspect is also of major concern in the development of polymeric materials used in aerospace applications. In fact, AO erosion has been recognized to be the most critical hazard for polymers exposed to the specific conditions of the Low Earth Orbit, where most satellites orbit. At these altitudes, AO, mainly formed via VUV photodissociation of O2, represents 80% of the residual atmosphere and acts as a hydrocarbon-degrading agent. Similar processes may potentially take place in the Low Mars Orbit, where the photodissociation of carbon dioxide produces a considerable amount of AO. Furthermore, along with other oxidizing agents in the Martian atmosphere, O atoms and OH radicals could be the chemical oxidizing agents responsible for the depletion of organics. This may justify the failure to find organic compounds on the Martian surface. Notably, the Curiosity rover has recently detected chlorinated aromatic compounds on the Martian surface, namely, chlorobenzene and dichlorobenzene. Thiophene, another aromatic species containing sulfur, has also been identified on Mars. More in general, processes induced by AO can also involve other refractory forms of carbon (amorphous graphite or large polycyclic aromatic hydrocarbons) that are abundant in our galaxy.
In this framework, following the study already carried out by the Perugia group on many O(3P) + aliphatic hydrocarbons reactions,1 we have started a systematic investigation of the reactions of AO with small aromatic compounds, namely, benzene,2 pyridine,3 and toluene.4 We have exploited the crossed molecular beam technique with mass-spectrometric detection and time-of-flight (TOF) analysis to unveil the primary reaction products, their relative yields (branching fractions, BFs), and the reaction micro-mechanism. The interpretation of the experimental results has been supported by high-level electronic structure calculations of potential energy surfaces (PESs) and RRKM/Master Equation computations of product BFs. In particular, for the reactions between O(3P) and benzene/pyridine, two main groups of mechanisms were observed: (i) the H-displacement channels, in which the oxygen atom replaces a H atom and (ii) the ring-contraction channels, leading to CO.2,3 Remarkably, the presence of the N atom in the aromatic ring of pyridine increases the probability of the ring-contraction mechanism.3 On the contrary, the presence of a methyl group attached to the aromatic ring, as in the case of toluene, allows preserving the six-member aromatic ring in the reaction products.4 The possible implications for the chemistry of different extraterrestrial environments will be noted.
Acknowledgments
We acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 1409 published on 14.09.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU – Project Title P20223H8CK Degradation of space-technology polymers by thermospheric oxygen atoms and ions: an exploration of the reaction mechanisms at an atomistic level (ThermOPoly) – CUP J53D23014440001 – Grant Assignment Decree No. 1386 adopted on 01.09.2023 by the Italian Ministry of Ministry of University and Research (MUR).
References
[1] H. Pan, et al., Chem. Soc. Rev., 46, 7517-7547 (2017).
[2] G. Vanuzzo, et al., J. Phys. Chem A, 125, 8434-8453 (2021).
[3] P. Recio, et al., Nat. Chem., 14, 1405-1412 (2022).
[4] N. Balucani, et al., Faraday Discuss., 2024, DOI: 10.1039/D3FD00181D.
How to cite: Pannacci, G., Vanuzzo, G., Recio, P., Caracciolo, A., Casavecchia, P., and Balucani, N.: Atomic oxygen as degrading agent in space organic chemistry: the case of O(3P) + small aromatics reactions, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-536, 2024.
In both terrestrial and extraterrestrial environments, polycyclic aromatic hydrocarbons (PAHs) are widespread, driving extensive interdisciplinary research.1,2 They play a significant role in the chemical evolution of the interstellar medium (ISM) and are considered a crucial reservoir of interstellar carbon. The presence of PAHs is inferred from the unidentified infrared (UIR) emission bands (3-14 µm) and the diffuse interstellar bands (DIBs), although the identification of individual PAH molecules remains a great challenge.
This broad interest stems from the need to understand the complex pathways leading to PAH formation from their atomic and radical constituents. Central to PAH synthesis is the phenyl radical (C6H5) in its 2A1 ground electronic state, recognized as a key transient species. This has prompted comprehensive investigations into C6H5 reactions with unsaturated hydrocarbons from both theoretical and experimental perspectives.3-5 Recently, our focus shifted to exploring the potential of the reaction between C6H5 and 1,3 butadiene as a pathway for producing C10H10 isomers, indene, and styrene.
Using the crossed molecular beam (CMB) scattering technique, combined with mass spectrometric detection and time-of-flight analysis, we meticulously identified primary products and their relative yields (branching fractions, BFs), elucidating the reaction micro-mechanism. Notably, at a collision energy of 141 kJ/mol, we observed the dominance of H-displacement channels, yielding C10H10 + H (BF = 0.77). By comparing our findings with previous CMB experiments and theoretical calculations of the C10H10 potential energy surface, we highlighted the significance of 1-phenyl-cis/trans-1,3-butadiene isomeric products.
Remarkably, our investigation uncovered, for the first time under single collision conditions, the presence of the styrene + vinyl product channel (BF = 0.23). The interest in the styrene molecule arises from its capability to react with another phenyl radical, thereby contributing to the formation of larger PAHs through PAH growth processes. This phenomenon occurs in warm regions of the ISM, such as the circumstellar envelopes of carbon-rich stars like IRC+10216, and proto-planetary nebulae like CRL 618.6
Acknowledgments: We acknowledge financial support under the National Recovery and Resilience Plan (NRRP), Mission 4, Component 2, Investment 1.1, Call for tender No. 104 published on 02.02.2022 by the Italian Ministry of University and Research (MUR), funded by the European Union – NextGenerationEU– Project Title 20227W5CLJ Biomass gasification for hydrogen production (Bio4H2) – CUP J53D23001970006 - Grant Assignment Decree No. 961 adopted on 30.06.2023 by the Italian Ministry of Ministry of University and Research (MUR) and P.C. acknowledges the European Union – NewxtGenerationEU under the Italian Ministry of University and Research (MUR) National Innovation Ecosystem grant ECS0000041 – VITALITY. CUP: B43C22000470005.
References
[1] A. M. Nienow and J.T Roberts, Ann. Rev. Phys. Chem., 57 105-128 (2006).
[2] R.I. Kaiser et al., Ann. Rev. Phys. Chem., 66 43-67 (2015).
[3] J.H. Seinfeld and J.F. Pankow, Ann. Rev. Phys. Chem., 54 121-140 (2003).
[4] A.M. Mebel et al., J. Phys. Chem. A, 121 901-926 (2017) (and references therein).
[5] X. Gu et al., J. Phys. Chem. A, 113 998-1006 (2009) (and references therein).
[6] J. Cernicharo et al., Astrophys. J., 546, L123-L126 (2001).
How to cite: Vanuzzo, G., Pannacci, G., Casavecchia, P., and Balucani, N.: Elucidating the Formation of Styrene via the Gas-Phase Reaction of the Phenyl Radical with 1,3 Butadiene Under Single Collision Conditions, Europlanet Science Congress 2024, Berlin, Germany, 8–13 Sep 2024, EPSC2024-727, 2024.
