Theoretical distribution of the Ammonia binding energy at interstellar icy grains : a new computational framework
Tinacci, Lorenzo (Università degli Studi di Torino. Dipartimento di Chimica)
Germain, Aurèle (Università degli Studi di Torino. Dipartimento di Chimica)
Pantaleone, Stefano (Università degli Studi di Torino. Dipartimento di Chimica)
Ferrero, Stefano (Universitat Autònoma de Barcelona. Departament de Química)
Ceccarelli, Cecilia (Centre National de la Recherche Scientifique. Université Grenoble Alpes. Institut de Planétologie et d'Astrophysique de Grenoble)
Ugliengo, Piero (Università degli Studi di Torino. Dipartimento di Chimica)

Data:	2022
Resum:	The binding energies (BE) of molecules on the interstellar grains are crucial in the chemical evolution of the interstellar medium (ISM). Both temperature-programmed desorption (TPD) laboratory experiments and quantum chemistry computations have often provided, so far, only single values of the BE for each molecule. This is a severe limitation, as the ices enveloping the grain mantles are structurally amorphous, giving rise to a manifold of possible adsorption sites, each with different BEs. However, the amorphous ice nature prevents the knowledge of structural details, hindering the development of a common accepted atomistic icy model. In this work, we propose a computational framework that closely mimics the formation of the interstellar grain mantle through a water by water accretion. On that grain, an unbiased random (but well reproducible) positioning of the studied molecule is then carried out. Here we present the test case of NH, a ubiquitous species in the molecular ISM. We provide the BE distribution computed by a hierarchy approach, using the semiempirical xTB-GFN2 as a low-level method to describe the whole icy cluster in combination with the B97D3 DFT functional as a high-level method on the local zone of the NH interaction. The final ZPE-corrected BE is computed at the ONIOM(DLPNO-CCSD(T)//B97D3:xTB-GFN2) level, ensuring the best cost/accuracy ratio. The main peak of the predicted NH BE distribution is in agreement with experimental TPD and computed data in the literature. A second broad peak at very low BE values is also present, which has never been detected before. It may provide the solution to a longstanding puzzle about the presence of gaseous NH also observed in cold ISM objects.
Ajuts:	European Commission 811312 European Commission 741002
Drets:	Aquest document està subjecte a una llicència d'ús Creative Commons. Es permet la reproducció total o parcial, la distribució, la comunicació pública de l'obra i la creació d'obres derivades, fins i tot amb finalitats comercials, sempre i quan es reconegui l'autoria de l'obra original.
Llengua:	Anglès
Document:	Article ; recerca ; Versió publicada
Matèria:	Amorphous water ice ; Xtb-gfn2 ; ONIOM ; DLPNO ; B97D3 ; NH adsorption ; NH binding energy
Publicat a:	ACS earth and space chemistry, Vol. 6 (June 2022) , p. 1514-1526, ISSN 2472-3452

DOI: 10.1021/acsearthspacechem.2c00040
PMID: 35747467

13 p, 10.1 MB

El registre apareix a les col·leccions:
Articles > Articles de recerca
Articles > Articles publicats