2020/10/18 by Giulia M. Bovolenta, Giulia Bovolenta, S. Bovino +14 · 3 citations
Chemistry · Earth and Planetary Sciences · Physics and Astronomy · #Astrophysics and Star Formation Studies #Astrophysics of Galaxies (astro-ph.GA) #Atmospheric Ozone and Climate #FOS: Physical sciences #Molecular Spectroscopy and Structure #astro-ph.GA
paper · pdf · doi:10.48550/arxiv.2010.09138
12 pages, 9 figures, 6 tables, accepted to Mol. Astrophys
arxiv created 2020/10/18 · openalex publication_date 2020/10/18 · arxiv updated 2020/10/20 · openalex created_date 2022/07/25 · openalex updated_date 2026/07/28
The knowledge of the binding energy of molecules on astrophysically relevant ices can help to obtain an estimate of the desorption rate, i.e. the molecules residence time on the surface. This represents an important parameter for astrochemical models, crucial to determine the chemical fate of complex organic molecules formed on dust grains and observed in the densest regions of the interstellar medium. In this work, we propose a new robust procedure to study the interaction of atoms and molecules with interstellar ices, based on ab initio molecular dynamics and density functional theory, validated by high-level ab initio methods at a CCSD(T)/CBS level. We have applied this procedure to hydrogen fluoride (HF), a promising tracer of the molecular content of galaxies. In total we found 13 unique equilibrium structures of HF binding to small water clusters of up to 4 molecules, with binding energies ranging from 1208 to 7162 K. We computed a 22-molecules model of amorphous solid water (ASW) surface using ab initio molecular dynamics simulations and carried out a systematic analysis of the binding sites of HF, in terms of binding modes and binding energies. Considering 10 different water clusters, we found a binding energy distribution with an average value of 5313±74 K, and a dispersion of 921±115 K. Finally, the effect of the electrostatic field of the 22 water molecules on the binding energies was investigated incrementally by symmetry adapted perturbation theory, in order to gauge the effect of the water environment. The results indicate that the extent of the electrostatic interaction of HF with ASW depends strongly on the properties of the binding site. We expect that this work will provide a solid foundation for a systematic development of a binding energy distribution database of molecules on interstellar surfaces.