For many years, the recombination of excited ions of argon, Ar+(P1/22), has been assumed negligible under ambient conditions as compared to the recombination of ground-state ions, Ar+(P3/22). This opinion was confronted with detailed experimental results that seem to clearly support it. Here, we propose a new interpretation in light of our recent calculations, which shows that the recombination efficiency is comparable for both fine-structure states. Noteworthily, in our model leading to a picture consistent with the experiment, residual dimer ions emerge from Ar+(P1/22) due to non-adiabatic dynamics effects and interplay in measured data.

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A general scheme for calculating ternary recombination rate constants of atomic species based on a hybrid quantum–classical nonadiabatic dynamics approach is presented and applied to the specific case of the ternary recombination of atomic ions of argon in cold argon plasmas. Rate constants are reported for both fine-structure states of the ion, and , T = 300 K, and for selected values of the reduced electric field. A thorough comparison with the literature data available for T = 300 K and a couple of close temperatures is performed with a favorable agreement achieved. It is shown that the excited ions may contribute to the formation of dimer ions, , as efficiently as the ground-state ions, , due to fast internal conversion of the electronic energy, which takes place in ternary collision complexes, .

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Formation, distribution and behaviour of Complex Organic Molecules (COM's) in space is an important subject of research to the better understanding of the initial condition for the appearance of life on Earth. Furthermore, the study of high energy chemical processes in the interstellar medium (cosmic radiation's effect) and in solar system (solar wind's effect), is been of high interest. The aim of this work is to study astrophysical molecules trapped in interstellar ice systems under the effect of high energy radiation. These ices are characterised by being large systems, with large number of atoms. QM/MM hybrid method has become a very popular tool for molecular systems' simulations with a large number of atoms, appearing as a good compromise between accuracy and computational costs. We report the implementation of QM/MM hybrid method in the deMonNano software, using the Density Functional based Tight Binding (DFTB), an approximated DFT scheme, combined with Molecular Mechanic (MM) approach, namely Force Fields (FF) of class 1, such as OPLS-AA and AMBER-families of FFs. A complete implementation was performed using the QM/MM additive coupling scheme. In addition, the investigation of high energy chemical processes requires the explicit simulation of the electronic dynamics beyond the Born Oppenheimer approximation. As first step towards such dynamics, we will report the implementation of Real Time TD-DFTB in deMonNano, consisting in solving the Time-Dependent Schrödinger equation within the DFTB, where the electronic density matrix is propagated along time. We report a detailed introduction to new DFTB/MM and RT-TD-DFTB implementations as well as the complete study on glycine prebiotic molecule trapped in an interstellar ice. PAH interstellar systems will be also a matter of study.

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Fullerene C 60 is one of the most iconic forms of carbon found in the interstellar medium (ISM). The interstellar chemistry of carbon-rich components, including fullerenes, is driven by a variety of energetic processes including UV and X-ray irradiation, cosmic-ray (CR) bombardment, electron impact, and shock waves. These violent events strongly alter the particle phase and lead to the release of new molecular species in the gas phase. Only a few experimental studies on the shock processing of cosmic analogs have been conducted so far. We explored in the laboratory the destruction of buckminsterfullerene C 60 using a pressure-driven shock tube coupled with optical diagnostics. Our efforts were first devoted to probing in situ the shock-induced processing of C 60 at high temperatures (≤ 4500 K) by optical emission spectroscopy. The analysis of the spectra points to the massive production of C 2 units. A broad underlying continuum was observed as well and was attributed to the collective visible emission of carbon clusters, generated similarly in large amounts. This proposed assignment was performed with the help of calculated emission spectra of various carbon clusters. The competition between dissociation and radiative relaxation, determined by statistical analysis, alludes to a predominance of clusters with less than 40 carbon atoms. Our laboratory experiments, supported by molecular dynamics simulations performed in the canonical ensemble, suggest that C 60 is very stable, and that high-energy input is required to process it under interstellar low-density conditions and to produce C 2 units and an abundance of intermediate-sized carbon clusters. These results provide some insights into the life cycle of carbon in space. Our findings hint that only J-type shocks with velocities above ~100 km s −1 or C-type shocks with velocities above 9 km s −1 can lead to the destruction of fullerenes. Observational tracers of this process remain elusive, however. Our work confirms the potential of shock tubes for laboratory astrophysics.

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