Germán Molpeceres

We report new computational and experimental evidence of an efficient and astrochemically relevant formation route to formaldehyde (H₂CO). This simplest carbonylic compound is central to the formation of complex organics in cold interstellar clouds and is generally regarded to be formed by the hydrogenation of solid-state carbon monoxide. We demonstrate H₂CO formation <i>via</i> the reaction of carbon atoms with amorphous solid water. Crucial to our proposed mechanism is a

Water is one of the most abundant molecules in the form of solid ice phase in the different regions of the interstellar medium (ISM). This large abundance cannot be properly explained by using only traditional low temperature gas-phase reactions. Thus, surface chemical reactions are believed to be major synthetic channels for the formation of interstellar water ice. Among the different proposals, hydrogenation of atomic O (<i>i.e.</i>, 2H + O → H₂O) is a chemically "simple" and plausi

ABSTRACT Dynamics of adsorption and desorption of (4S)-N on amorphous solid water are analysed using molecular dynamic simulations. The underlying potential energy surface was provided by machine-learned interatomic potentials. Binding energies confirm the latest available theoretical and experimental results. The nitrogen sticking coefficient is close to unity at dust temperatures of 10 K but decreases at higher temperatures. We estimate a desorption time-scale of 1 μs at 28 K. The estimated ti

Context. Energy redistribution after a chemical reaction is one of the few mechanisms that can explain the diffusion and desorption of molecules which require more energy than the thermal energy available in quiescent molecular clouds (10 K). This energy distribution can be important in phosphorous hydrides, elusive yet fundamental molecules for interstellar prebiotic chemistry. Aims . Our goal with this study is to use state-of-the-art methods to determine the fate of the chemical energy in the

Context. Recent interstellar detections include a significant number of molecules containing vinyl (C 2 H 3 ) and ethyl (C 2 H 5 ) groups in their structure. For several of these molecules, there is no clear experimental or theoretical evidence that supports their formation from simpler precursors. Aims. We carried out a systematic search of viable reactions starting from closed-shell hydrocarbons containing two carbon atoms (ethane, C 2 H 6 ; ethylene, C 2 H 4 ; and acetylene, C 2 H 2 ), with t

Abstract With the presence of evermore complex S-bearing molecules being detected lately, studies of their chemical formation routes need to keep up the pace to rationalize observations, suggest new candidates for detection, and provide input for chemical evolution models. In this paper, we theoretically characterize the hydrogenation channels of OCS on top of amorphous solid water (ASW) as an interstellar dust grain analog in molecular clouds. Our results show that the significant reaction outc

Context. The isomerism of molecules in the interstellar medium and the mechanisms behind it are essential questions in the chemistry of organic molecules in space. In the particular case of simple formic and thioformic acids, the low temperatures found in molecular clouds indicate that cis-trans isomerization in the gas-phase must be impeded. Reactions taking place on top of interstellar dust grains may explain the isomer interconversion at low temperatures. Aims. We studied the isomerization pr

A theoretical study of the structure and mid infrared (IR) spectra of interstellar hydrocarbon dust analogs is presented, based on DFT calculations of amorphous solids. The basic molecular structures for these solids are taken from two competing literature models. The first model considers small aromatic units linked by aliphatic chains. The second one assumes a polyaromatic core with hydrogen and methyl substituents at the edges. The calculated spectra are in reasonably good agreement with thos

Abstract The detection of phosphorous-bearing molecules in interstellar environments constitutes a fundamental task for understanding the formation of prebiotic molecules, but it is also a challenge. In cold interstellar environments, where rich chemistry is expected to happen, only PN and PO have been detected. Phosphine (PH 3 ) must also play an essential role in these regions, since P is expected to deplete onto dust grains significantly, and hydrogenation reactions are dominant in such envir

ABSTRACT The recent wave of detections of interstellar aromatic molecules has sparked interest in the chemical behaviour of aromatic molecules under astrophysical conditions. In most cases, these detections have been made through chemically related molecules, called proxies, that implicitly indicate the presence of a parent molecule. In this study, we present the results of the theoretical evaluation of the hydrogenation reactions of different aromatic molecules (benzene, pyridine, pyrrole, fura

ABSTRACT We present a spectroscopic study of methane–ethane ice mixtures. We have grown CH 4 :C 2 H 6 mixtures with ratios 3:1, 1:1, and 1:3 at 18 and 30 K, plus pure methane and ethane ices, and have studied them in the near-infrared (NIR) and mid-infrared (MIR) ranges. We have determined densities of all species mentioned above. For amorphous ethane grown at 18 and 30 K we have obtained a density of 0.41 and 0.54 g cm −3 , respectively, lower than a previous measurement of the density of the c

Context . Carbon dioxide (CO 2 ) is one of the dominant components of interstellar ices. Recent observations show CO 2 exists more abundantly in polar (H 2 O-dominated) ice than in apolar (H 2 O-poor) ice. Formation of CO 2 ice is primarily attributed to the reaction between CO and OH, which has a barrier. Aims . We investigate the title reaction in H 2 O ice and CO ice to quantify the efficiency of the reaction in polar ice and apolar ice. Methods . Highly accurate quantum chemical calculations

Context. Molecular hydrogen (H 2 ) is the most abundant interstellar molecule and plays an important role in the chemistry and physics of the interstellar medium. The interaction of H 2 with interstellar ices is relevant for several processes (e.g., nuclear spin conversion and chemical reactions on the surface of the ice). To model surface processes, quantities such as binding energies and sticking coefficients are required. Aims. We provide sticking coefficients and binding energies for the H 2

The recent discovery of the nature and behavior of carbon atoms interacting with interstellar ices has prompted a number of investigations on the chemistry initiated by carbon accretion on icy interstellar dust. In this work, we expand the range of processes promoted by carbon accretion to the chemistry initiated by the interaction of this atom with ammonia (NH₃) using quantum chemical calculations. We found that carbon addition to the ammonia molecule forms a rather stable radical, C

Context. Explaining the presence of complex organic molecules (COMs) in interstellar environments requires a thorough understanding of the physics and chemistry occurring in the interplay between the gas phase and interstellar surfaces. Experiments and computer simulations are pivotal in building a comprehensive catalogue of processes of relevance for the build up of organic molecules in those environments. Aims. We combine experiments with tailored computer simulations to study the desorption d