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Tinacci L, Germain A, Pantaleone S, Ferrero S, Ceccarelli C, Ugliengo P. Theoretical Distribution of the Ammonia Binding Energy at Interstellar Icy Grains: A New Computational Framework. ACS EARTH & SPACE CHEMISTRY 2022; 6:1514-1526. [PMID: 35747467 PMCID: PMC9208021 DOI: 10.1021/acsearthspacechem.2c00040] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 02/05/2022] [Revised: 05/19/2022] [Accepted: 05/19/2022] [Indexed: 06/15/2023]
Abstract
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 NH3, 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 NH3 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 NH3 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 NH3 also observed in cold ISM objects.
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Affiliation(s)
- Lorenzo Tinacci
- Dipartimento
di Chimica, Università degli Studi
di Torino, via P. Giuria
7, 10125 Torino, Italy
- Institut
de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France
| | - Auréle Germain
- Dipartimento
di Chimica, Università degli Studi
di Torino, via P. Giuria
7, 10125 Torino, Italy
| | - Stefano Pantaleone
- Dipartimento
di Chimica, Università degli Studi
di Torino, via P. Giuria
7, 10125 Torino, Italy
- Dipartimento
di Chimica, Biologia e Biotecnologie, Università
degli Studi di Perugia, 06123 Perugia, Italy
| | - Stefano Ferrero
- Departament
de Quimica, Universitat Autònoma
de Barcelona, 08193 Bellaterra, Catalonia Spain
| | - Cecilia Ceccarelli
- Institut
de Planétologie et d’Astrophysique de Grenoble (IPAG), 38000 Grenoble, France
| | - Piero Ugliengo
- Dipartimento
di Chimica, Università degli Studi
di Torino, via P. Giuria
7, 10125 Torino, Italy
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Schmidt MR, He JH, Szczerba R, Bujarrabal V, Alcolea J, Cernicharo J, Decin L, Justtanont K, Teyssier D, Menten KM, Neufeld DA, Olofsson H, Planesas P, Marston AP, Sobolev AM, de Koter A, Schöier FL. Herschel/HIFI observations of the circumstellar ammonia lines in IRC+10216. ASTRONOMY AND ASTROPHYSICS 2016; 592:A131. [PMID: 28065983 PMCID: PMC5217166 DOI: 10.1051/0004-6361/201527290] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/06/2023]
Abstract
CONTEXT A discrepancy exists between the abundance of ammonia (NH3) derived previously for the circumstellar envelope (CSE) of IRC+10216 from far-IR submillimeter rotational lines and that inferred from radio inversion or mid-infrared (MIR) absorption transitions. AIMS To address the discrepancy described above, new high-resolution far-infrared (FIR) observations of both ortho- and para-NH3 transitions toward IRC+10216 were obtained with Herschel, with the goal of determining the ammonia abundance and constraining the distribution of NH3 in the envelope of IRC+10216. METHODS We used the Heterodyne Instrument for the Far Infrared (HIFI) on board Herschel to observe all rotational transitions up to the J = 3 level (three ortho- and six para-NH3 lines). We conducted non-LTE multilevel radiative transfer modelling, including the effects of near-infrared (NIR) radiative pumping through vibrational transitions. The computed emission line profiles are compared with the new HIFI data, the radio inversion transitions, and the MIR absorption lines in the ν2 band taken from the literature. RESULTS We found that NIR pumping is of key importance for understanding the excitation of rotational levels of NH3. The derived NH3 abundances relative to molecular hydrogen were (2.8 ± 0.5) × 10-8 for ortho-NH3 and [Formula: see text] for para-NH3, consistent with an ortho/para ratio of 1. These values are in a rough agreement with abundances derived from the inversion transitions, as well as with the total abundance of NH3 inferred from the MIR absorption lines. To explain the observed rotational transitions, ammonia must be formed near to the central star at a radius close to the end of the wind acceleration region, but no larger than about 20 stellar radii (1σ confidence level).
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Affiliation(s)
- M. R. Schmidt
- N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland
| | - J. H. He
- Key Laboratory for the Structure and Evolution of Celestial Objects, Yunnan Observatories, Chinese Academy of Sciences, P.O. Box 110, Kunming, Yunnan Province, China
| | - R. Szczerba
- N. Copernicus Astronomical Center, Rabiańska 8, 87-100 Toruń, Poland
| | - V. Bujarrabal
- Observatorio Astronómico Nacional. Ap 112, E-28803 Alcalá de Henares, Spain
| | - J. Alcolea
- Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, E-28014 Madrid, Spain
| | - J. Cernicharo
- ICMM, CSIC, group of Molecular Astrophysics, C/Sor Juana Inés de la Cruz N3, 28049 Cantoblanco (Madrid), Spain
| | - L. Decin
- Instituut voor Sterrenkunde, Katholieke Universiteit Leuven, Celestijnenlaan 200D, 3001 Leuven, Belgium
- Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam, The Netherlands
| | - K. Justtanont
- Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden
| | - D. Teyssier
- European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid, Spain
| | - K. M. Menten
- Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, D-53121 Bonn, Germany
| | | | - H. Olofsson
- Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden
- Department of Astronomy, AlbaNova University Center, Stockholm University, SE–10691 Stockholm, Sweden
| | - P. Planesas
- Observatorio Astronómico Nacional (IGN), Alfonso XII N°3, E-28014 Madrid, Spain
| | - A. P. Marston
- European Space Astronomy Centre, ESA, P.O. Box 78, E-28691 Villanueva de la Cañada, Madrid, Spain
| | - A. M. Sobolev
- Ural Federal University, Astronomical Observatory, 620000 Ekaterinburg, Russian Federation
| | - A. de Koter
- Sterrenkundig Instituut Anton Pannekoek, University of Amsterdam, Science Park 904, NL-1098 Amsterdam, The Netherlands
| | - F. L. Schöier
- Chalmers University of Technology, Department of Earth and Space Sciences, Onsala Space Observatory, S-439 92 Onsala, Sweden
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