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Richardson V, Valença Ferreira de Aragão E, He X, Pirani F, Mancini L, Faginas-Lago N, Rosi M, Martini LM, Ascenzi D. Fragmentation of interstellar methanol by collisions with He˙ +: an experimental and computational study. Phys Chem Chem Phys 2022; 24:22437-22452. [PMID: 36102850 DOI: 10.1039/d2cp02458f] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Methanol is a key species in astrochemistry as its presence and reactivity provides a primary route to the synthesis of more complex interstellar organic molecules (iCOMs) that may eventually be incorporated in newly formed planetary systems. In the interstellar medium, methanol is formed by hydrogenation of CO ices on grains, and its fate upon collisions with interstellar ions should be accounted for to correctly model iCOM abundances in objects at various stages of stellar evolution. The absolute cross sections (CSs) and branching ratios (BRs) for the collisions of He˙+ ions with CH3OH are measured, as a function of the collision energy, using a Guided Ion Beam Mass Spectrometer (GIB-MS). Insights into the dissociative electron (charge) exchange mechanism have been obtained by computing the entrance and exit multidimensional Potential Energy Surfaces (PESs) and by modelling the non-adiabatic transitions using an improved Landau-Zener-Stückelberg approach. Notably, the dynamical treatment reproducing the experimental findings includes a strong orientation effect of the system formed by the small He˙+ ion and the highly polar CH3OH molecule, in the electric field gradient associated to the strongly anisotropic intermolecular interaction. This is a stereodynamical effect that plays a fundamental role in collision events occurring under a variety of conditions, with kinetic energy confined within intervals ranging from the sub-thermal to the hyper-thermal regime.
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Affiliation(s)
| | - Emília Valença Ferreira de Aragão
- Department of Chemistry, Biology and Biotechnology, Università degli studi di Perugia, Perugia, Italy.,Master-Tec s.r.l., Via Sicilia 41, Perugia, Italy
| | - Xiao He
- Department of Physics, University of Trento, Trento, Italy.
| | - Fernando Pirani
- Department of Chemistry, Biology and Biotechnology, Università degli studi di Perugia, Perugia, Italy.,Department of Civil and Environmental Engineering, Università degli studi di Perugia, Perugia, Italy
| | - Luca Mancini
- Department of Chemistry, Biology and Biotechnology, Università degli studi di Perugia, Perugia, Italy
| | - Noelia Faginas-Lago
- Department of Chemistry, Biology and Biotechnology, Università degli studi di Perugia, Perugia, Italy.,Master-Tec s.r.l., Via Sicilia 41, Perugia, Italy
| | - Marzio Rosi
- Department of Civil and Environmental Engineering, Università degli studi di Perugia, Perugia, Italy
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Chin CH, Zhu T, Zhang JZH. Cyclopentadienyl radical formation from the reaction of excited nitrogen atoms with benzene: a theoretical study. Phys Chem Chem Phys 2021; 23:12408-12420. [PMID: 34027937 DOI: 10.1039/d1cp00133g] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Ab initio CCSD(T)/CBS//ωB97X-D/6-311+G(d,p) calculations of the C6H6N potential energy surface were performed to investigate the reaction mechanism underlying the reaction of atomic nitrogen (2D) with benzene. Thereafter, Rice-Ramsperger-Kassel-Marcus (RRKM) calculations of reaction rate constants and product branching ratios were performed under single-collision conditions. The results revealed that the N(2D) + C6H6 reaction in the case of statistical behavior is expected to produce hydrogen cyanide plus a cyclopentadienyl radical (91.5-88.9%), acetylene plus a pyrrole radical (5.8-7.5%), 1-cyano-2,4-cyclopentadiene + H (2.3-3.0%) and 1-ethynyl-pyrrole + H (0.4-0.6%), with the most favorable pathways being the initial adduct i1 leading to the formation of a seven-membered cyclic intermediate i12 through an exothermic ring expansion process and a multistep route i12 → i15 → i16 → C5H5 + HCN featuring an intramolecular ring-shrinking process involving a C-C bond fusion elimination channel to yield the bicyclic intermediate i15, followed by hydrogen cyanide elimination, thus forming a cyclopentadienyl radical. The calculated product branching ratios were consistent with the available experimental data; however, some quantitative deviations from the experimental results and the possible reasons are also discussed. The possible effects of the title reaction on the upper atmosphere of Titan, with critical implications for the rapid degradation of nitrogen-bearing polycyclic aromatic hydrocarbons, were compared with the mass growth processes of their polycyclic aromatic hydrocarbon counterparts produced through ring expansion.
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Affiliation(s)
- Chih-Hao Chin
- School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, China. and NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai, 200062, China.
| | - Tong Zhu
- School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, China. and NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai, 200062, China.
| | - John Zeng Hui Zhang
- School of Chemistry and Molecular Engineering, East China Normal University, Shanghai, 200062, China. and NYU-ECNU Center for Computational Chemistry at NYU Shanghai, Shanghai, 200062, China. and Department of Chemistry, New York University, New York 10003, USA
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