Predictive simulations of core electron binding energies of halogenated species adsorbed on ice surfaces from relativistic quantum embedding calculations (original) (raw)
Related papers
Molecular Simulation, 2018
In this paper, we present a brief review of what has been learned about the adsorption characteristics of various organic molecules at the surface of ice, from more than 15 years of computer simulation studies at the molecular scale. In particular, grand canonical Monte Carlo and molecular dynamics calculations were performed to determine the adsorption isotherms, the saturation coverage of the first molecular layer at the ice surface, the preferred orientations of the molecules in their adsorption sites, and the corresponding adsorption energies. The results of the simulations indicated that the main driving force for trace gas adsorption on ice is hydrogen bonding not only between the adsorbate and the water molecules of the ice surface, but also within the adsorbate. When possible, the comparison with available experimental data showed a close agreement, supporting thus the methodology used in the modelling. Finally, the present review demonstrates how computer simulation can nicely complement experimental approaches for studying interactions between trace gases and ice under tropospheric and interstellar condition
Springer eBooks, 2022
The interstellar medium is extremely heterogeneous in terms of physical environments and chemical composition. Spectroscopic observations in the recent decades have revealed the presence of gaseous material and dust grains covered in ices predominantly of water in interstellar clouds, the interplay of which may elucidate the existence of more than 250 molecular species. Of these species of varied complexity, several terrestrial carbon-containing compounds have been discovered, known as interstellar complex organic molecules (iCOMs) in the astrochemical argot. In order to investigate the formation of iCOMs, it is crucial to explore gas-grain chemistry and in this regard, one of the fundamental parameters is the binding energy (BE), which is an essential input in astrochemical models. In this work, the BEs of 13 iCOMs on a crystalline H 2 O-ice surface have been computed by means of quantum chemical periodic calculations. The hybrid B3LYP-D3 DFT method was used for the geometry optimizations of the adsorbate/ice systems and for computing the BEs. Furthermore, to refine the BE values, an ONIOM2-like approximation has been employed to obtain them at CCSD(T), which correlate well with those obtained at B3LYP-D3. Additionally, aiming to lower the computational cost, structural optimizations were carried out using the HF-3c level of theory, followed by single point energy calculations at B3LYP-D3 in order to obtain BE values comparable to the full DFT treatment.
Binding Energy of Molecules on Water Ice: Laboratory Measurements and Modeling
The Astrophysical Journal, 2016
We measured the binding energy of N 2 , CO, O 2 , CH 4 , and CO 2 on non-porous (compact) amorphous solid water (np-ASW), of N 2 and CO on porous amorphous solid water (p-ASW), and of NH 3 on crystalline water ice. We were able to measure binding energies down to a fraction of 1% of a layer, thus making these measurements more appropriate for astrochemistry than the existing values. We found that CO 2 forms clusters on np-ASW surface even at very low coverages. The binding energies of N 2 , CO, O 2 , and CH 4 decrease with coverage in the submonolayer regime. Their values at the low coverage limit are much higher than what is commonly used in gas-grain models. An empirical formula was used to describe the coverage dependence of the binding energies. We used the newly determined binding energy distributions in a simulation of gas-grain chemistry for cold cloud and hot core models. We found that owing to the higher value of desorption energy in the sub-monlayer regime a fraction of all these ices stays much longer and up to higher temperature on the grain surface compared to the single value energies currently used in the astrochemical models.
The Astrophysical Journal, 2020
In the denser and colder (≤20 K) regions of the interstellar medium (ISM), near-infrared observations have revealed the presence of sub-micron sized dust grains covered by several layers of H 2 O-dominated ices and "dirtied" by the presence of other volatile species. Whether a molecule is in the gas or solid-phase depends on its binding energy (BE) on ice surfaces. Thus, BEs are crucial parameters for the astrochemical models that aim to reproduce the observed evolution of the ISM chemistry. In general, BEs can be inferred either from experimental techniques or by theoretical computations. In this work, we present a reliable computational methodology to evaluate the BEs of a large set (21) of astrochemical relevant species. We considered different periodic surface models of both crystalline and amorphous nature to mimic the interstellar water ice mantles. Both models ensure that hydrogen bond cooperativity is fully taken into account at variance with the small ice cluster models. Density functional theory adopting both B3LYP-D3 and M06-2X functionals was used to predict the species/ice structure and their BEs. As expected from the complexity of the ice surfaces, we found that each molecule can experience multiple BE values, which depend on its structure and position at the ice surface. A comparison of our computed data with literature data shows agreement in some cases and (large) differences in others. We discuss some astrophysical implications that show the importance of calculating BEs using more realistic interstellar ice surfaces to have reliable values for inclusion in the astrochemical models.
Computational Science and Its Applications – ICCSA 2021, 2021
There are different environments in the interstellar medium (ISM), depending on the density, temperature and chemical composition. Among them, molecular clouds, often referred to as the cradle of stars, are paradigmatic environments relative to the chemical diversity and complexity in space. Indeed, there, radio to far-infrared observations revealed the presence of several molecules in the gas phase, while nearinfrared spectroscopy detected the existence of submicron sized dust grains covered by H 2 O-dominated ice mantles. The interaction between gas-phase species and the surfaces of water ices is measured by the binding energy (BE), a crucial parameter in astrochemical modelling. In this work, the BEs of a set of sulphur-containing species on water ice mantles have been computed by adopting a periodic ab initio approach using a crystalline surface model. The Density Functional Theory (DFT)-based B3LYP-D3(BJ) functional was used for the prediction of the structures and energetics. DFT BEs were refined by adopting an ONIOM-like procedure to estimate them at CCSD(T) level toward complete basis set extrapolation, in which a very good correlation between values has been found. Moreover, we show that geometry optimization with the computationally cheaper HF-3c method followed by single point energy calculations at DFT to compute the BEs is a suitable cost-effective recipe to arrive at BE values of the same quality as those computed at full DFT level. Finally, computed data were compared with the available literature data.
The Astrophysical Journal
Binding energies (BEs) are one of the most important parameters for astrochemical modeling determining, because they govern whether a species stays in the gas phase or is frozen on the grain surfaces. It is currently known that, in the denser and colder regions of the interstellar medium, sulfur is severely depleted in the gas phase. It has been suggested that it may be locked into the grain icy mantles. However, which are the main sulfur carriers is still a matter of debate. This work aims to establish accurate BEs of 17 sulfur-containing species on two validated water ice structural models, the proton-ordered crystalline (010) surface and an amorphous water ice surface. We adopted density functional theory-based methods (the hybrid B3LYP-D3(BJ) and the hybrid meta-GGA M06-2X functionals) to predict structures and energetics of the adsorption complexes. London’s dispersion interactions are shown to be crucial for an accurate estimate of the BEs due to the presence of the high polar...
SURVIVAL DEPTH OF ORGANICS IN ICES UNDER LOW-ENERGY ELECTRON RADIATION (⩽2 keV)
The Astrophysical Journal, 2012
Icy surfaces in our solar system are continually modified and sputtered with electrons, ions, and photons from solar wind, cosmic rays, and local magnetospheres in the cases of Jovian and Saturnian satellites. In addition to their prevalence, electrons specifically are expected to be a principal radiolytic agent on these satellites. Among energetic particles (electrons and ions), electrons penetrate by far the deepest into the ice and could cause damage to organic material of possible prebiotic and even biological importance. To determine if organic matter could survive and be detected through remote sensing or in situ explorations on these surfaces, such as water ice-rich Europa, it is important to obtain accurate data quantifying electron-induced chemistry and damage depths of organics at varying incident electron energies. Experiments reported here address the quantification issue at lower electron energies (100 eV-2 keV) through rigorous laboratory data analysis obtained using a novel methodology. A polycyclic aromatic hydrocarbon molecule, pyrene, embedded in amorphous water ice films of controlled thicknesses served as an organic probe. UV-VIS spectroscopic measurements enabled quantitative assessment of organic matter survival depths in water ice. Eight ices of various thicknesses were studied to determine damage depths more accurately. The electron damage depths were found to be linear, approximately 110 nm keV −1 , in the tested range which is noticeably higher than predictions by Monte Carlo simulations by up to 100%. We conclude that computational simulations underestimate electron damage depths in the energy region 2 keV. If this trend holds at higher electron energies as well, present models utilizing radiation-induced organic chemistry in icy solar system bodies need to be revisited. For interstellar ices of a few micron thicknesses, we conclude that low-energy electrons generated through photoionization processes in the interstellar medium could penetrate through ice grains significantly and trigger organic reactions several hundred nanometers deep-bulk chemistry thus competing with surface chemistry of astrophysical ice grains.
Electron contribution to photon-induced desorption in molecular ices
2023
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Electron impact ionization of H2O molecule in crystalline ice
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2003
The present work focuses on electron impact scattering in crystalline ice, which is an exotic solid. The major difference between crystalline form and amorphous form lies in its structure. Here we consider the H 2 O molecule to possess properties consistent with the ice structure. Our basic calculation rests on the complex optical potential for the e-molecule system, with the molecular charge density as an input. To examine a single scattering event in condensed phases, we build up a model scattering potential to determine total inelastic cross-section Q inel . Finally an estimate of the total ionization cross-section, Q ion for H 2 O (free), H 2 O (amorphous) and H 2 O (ice) in the energy range from threshold to 2000 eV, is obtained through semi-empirical arguments.
Electron impact ionization of water molecules in ice and liquid phases
Journal of Physics: Conference Series, 2007
In this paper we report comprehensive calculations of total elastic (Q el ), total ionization (Q ion ) and total (complete) cross sections (Q T ) for the impact of electrons on inert gases (He, Ne, Ar, Kr and Xe) at energies from about threshold to 2000 eV. We have employed the spherical complex optical potential (SCOP) formalism to evaluate Q el and Q T and used the complex spherical potentialionization contribution (CSP-ic) method to derive Q ion . The dependence of Q T on polarizability and incident energy is presented for these targets through an analytical formula. Mutual comparison of various cross sections is provided to show their relative contribution to the total cross sections Q T . Comparison of Q T for all these targets is carried out to present a general theoretical picture of collision processes. The present calculations also provide information, hitherto sparse, on the excitation processes of these atomic targets. These results are compared with available experimental and other theoretical data and overall good agreement is observed.