arXiv subjects

German Molpeceres

Publications and source records attributed to German Molpeceres.

4 recordsLinked to original sources

arXiv2026

Formation of adducts of C$_6$H with Na$^+$, Mg$^+$ and Al$^+$ metal cations by radiative association

The Mg-bearing cations MgC$_4$H$^+$, MgC$_6$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$ have been recently observed in the carbon-rich envelope IRC\,+10216. These species are thought to form upon radiative association between Mg$^+$ and the corresponding neutral radical. This work aims to determine the radiative association rate coefficients for the cations Al$^+$, Mg$^+$, and Na$^+$ reacting with carbon chain radicals to estimate the relative importance of metal-bearing carbon cations for each of these metals. For this purpose we use statistical methods in combination with highly accurate ab initio calculations to obtain the radiative association rate coefficient. Moreover, anisotropic effects beyond mono-dimensional capture model are considered, providing a more reliable description of the simulated processes.} The radiative association rate coefficients to form Mg-, Al- and Na-C$_6$H$^+$, as well as MgC$_4$H$^+$, MgC$_3$N$^+$, and MgC$_5$N$^+$, are calculated with the new restrictions considered in this work. These new rate coefficients are included in a chemical model of the C-rich AGB envelope IRC\,+10216. The abundances of MgC$_4$H$^+$, MgC$_6$H$^+$, and MgC$_5$N$^+$ are consistent with observations, with differences no greater than one order of magnitude, corroborating radiative association as a plausible formation mechanism for these adducts. However, the calculated abundance of MgC$_3$N$^+$ is about two orders of magnitude lower than observed, which indicates that either the chemistry of this species is significantly different from the others or the calculated rate coefficient is too low. The abundances obtained for Na-C$_6$H$^+$ and Al-C$_6$H$^+$ are around two orders of magnitude lower than for Mg, making very difficult to detect the analogous metal-bearing cations in IRC\,+10216.

astro-ph.SR↗

arXiv2025

The Emergence of Prebiotic Chemistry in the ISM

Contrary to popular belief, the interstellar medium (ISM) is not empty; it is filled with atoms, dust particles, and molecules. Some of these molecules may have been the very building blocks of life that, delivered to Earth via comets and meteorites, could have given rise to Life itself. A large-area single-dish telescope with superb sensitivity, field-of-view and multi-band instruments will allow us to explore the limits of chemical complexity in the interstellar medium, across our Galaxy and in external galaxies, determining whether amino acids, sugars, or RNA/DNA nucleobases can form in space.

astro-ph.IM↗

arXiv2024

In-Depth Exploration of Catalytic Sites on Amorphous Solid Water: I. The Astrosynthesis of Aminomethanol

Chemical processes taking place on ice-grain mantles are pivotal to the complex chemistry of interstellar environments. In this study, we conducted a comprehensive analysis of the catalytic effects of an amorphous solid water (ASW) surface on the reaction between ammonia (NH$_3$) and formaldehyde (H$_2$CO) to form aminomethanol (NH$_2$CH$_2$OH) using density functional theory. We identified potential catalytic sites based on the binding energy distribution of NH$_3$ and H$_2$CO reactants, on a set-of-clusters surface model composed of 22 water molecules and found a total of 14 reaction paths. Our results indicate that the catalytic sites can be categorized into four groups, depending on the interactions of the carbonyl oxygen and the amino group with the ice surface in the reactant complex. A detailed analysis of the reaction mechanism using Intrinsic Reaction Coordinate and reaction force analysis revealed three distinct chemical events for this reaction: formation of the C--N bond, breaking of the N--H bond, and formation of the O--H hydroxyl bond. Depending on the type of catalytic site, these events can occur within a single, concerted, albeit asynchronous, step, or can be isolated in a step-wise mechanism, with the lowest overall transition state energy observed at 1.3 kcal mol$^{-1}$. A key requirement for the low-energy mechanism is the presence of a pair of dangling OH bonds on the surface, found at 5\% of the potential catalytic sites on an ASW porous surface.

astro-ph.GA↗

arXiv2022

Radical Addition and H Abstraction Reactions in C2H2, C2H4 and C2H6: A Gateway for Ethyl and Vinyl Bearing Molecules in the Interstellar Medium

Recent interstellar detections include a significant number of molecules containing vinyl (C2H3) and ethyl (C2H5) groups in their structure. For several of these molecules, there is not a clear experimental or theoretical evidence that support their formation from simpler precursors. We carried out a systematic search of viable reactions starting from closed shell hydrocarbons containing two carbon atoms (ethane, C2H6; ethylene, C2H4; and acetylene, C2H2) with the goal of determining viable chemical routes for the formation of vinyl and ethyl molecules on top of interstellar dust grains. Our results show that both H and OH radicals are key in converting acetylene and ethylene into more complex radicals that are susceptible to continue reacting and forming interstellar complex organic molecules. The relevant reactions, for example OH additions, present rate constants above 10$^{1}$ s$^{-1}$ that are likely competitive with OH diffusion on grains. Similarly, H atom addition to acetylene and ethylene is a very fast process with rate constants above 10$^{4}$ s$^{-1}$ in all cases, and greatly enhanced by quantum tunneling. Hydrogen abstraction reactions are less relevant, but may play a role in specific cases involving the OH radical. Reactions with other radicals NH2, CH3 are likely to have a much lesser impact in the chemistry of ethyl and vinyl bearing molecules.

astro-ph.GA↗