Reactivity of the Ethenium Cation (C2H5+) with Ethyne (C2H2): A Combined Experimental and Theoretical Study

0584869 - ÚFCH JH 2025 RIV CH eng J - Článek v odborném periodiku
Richardson, V. - Polášek, Miroslav - Romanzin, C. - Tosi, P. - Thissen, R. - Alcaraz, C. - Žabka, Ján - Ascenzi, D.
Reactivity of the Ethenium Cation (C2H5+) with Ethyne (C2H2): A Combined Experimental and Theoretical Study.
Molecules. Roč. 29, č. 4 (2024), č. článku 810. E-ISSN 1420-3049
Grant CEP: GA MŠMT(CZ) LTC20062; GA ČR(CZ) GC21-11931J
Institucionální podpora: RVO:61388955
Klíčová slova: acetylene * Cassini mission * interstellar medium * ion–molecule reactions * planetary atmospheres * plasma * Titan
Obor OECD: Physical chemistry
Impakt faktor: 4.6, rok: 2022
Způsob publikování: Open access
https://www.mdpi.com/1420-3049/29/4/810

The gas-phase reaction between the ethyl cation (C2H5+) and ethyne (C2H2) is re-investigated by measuring absolute reactive cross sections (CSs) and branching ratios (BRs) as a function of collision energy, in the thermal and hyperthermal energy range, via tandem-guided ion beam mass spectrometry under single collision conditions. Dissociative photoionization of C2H5Br using tuneable VUV radiation in the range 10.5–14.0 eV is employed to generate C2H5+, which has also allowed us to explore the impact of increasing (vibrational) excitation on the reactivity. Reactivity experiments are complemented by theoretical calculations, at the G4 level of theory, of the relative energies and structures of the most relevant stationary points on the reactive potential energy hypersurface (PES) and by mass-analyzed ion kinetic energy (MIKE) spectrometry experiments to probe the metastable decomposition from the [C4H7]+ PES and elucidate the underlying reaction mechanisms. Two main product channels have been identified at a centre-of-mass collision energy of (Formula presented.) eV: (a) C3H3++CH4, with BR = 0.76 (Formula presented.) 0.05 and (b) C4H5++H2, with BR = 0.22 (Formula presented.) 0.02. A third channel giving C2H3+ in association with C2H4 is shown to emerge at both high internal excitation of C2H5+ and high collision energies. From CS measurements, energy-dependent total rate constants in the range (Formula presented.) (Formula presented.) − (Formula presented.) (Formula presented.)   (Formula presented.) (Formula presented.) (Formula presented.) have been obtained. Theoretical calculations indicate that both channels stem from a common covalently bound intermediate, CH3CH2CHCH+, from which barrierless and exothermic pathways exist for the production of both cyclic c−C3H3+ and linear H2CCCH+ isomers of the main product channel. For the minor C4H5+ product, two isomers are energetically accessible: the three-member cyclic isomer c−C3H2(CH3)+ and the higher energy linear structure CH2CHCCH2+, but their formation requires multiple isomerization steps and passages via transition states lying only 0.11 eV below the reagents’ energy, thus explaining the smaller BR. Results have implications for the modeling of hydrocarbon chemistry in the interstellar medium and the atmospheres of planets and satellites as well as in laboratory plasmas (e.g., plasma-enhanced chemical vapor deposition of carbon nanotubes and diamond-like carbon films).
Trvalý link: https://hdl.handle.net/11104/0352655