title: Selective Generation of the Radical Cation Isomers [CH3CN](•+) and [CH2CNH](•+) via VUV Photoionization of Different Neutral Precursors and Their Reactivity with C2H4.
abstract: Experimental and theoretical studies have been carried out to demonstrate the selective generation of two different C2H3N(+) isomers, namely, the acetonitrile [CH3CN](•+) and the ketenimine [CH2CNH](•+) radical cations. Photoionization and dissociative photoionization experiments from different neutral precursors (acetonitrile and butanenitrile) have been performed using vacuum ultraviolet (VUV) synchrotron radiation in the 10-15 eV energy range, delivered by the DESIRS beamline at the SOLEIL storage ring. For butanenitrile (CH3CH2CH2CN) an experimental ionization threshold of 11.29 ± 0.05 eV is obtained, whereas the appearance energy for the formation of [CH2CNH](•+) fragments is 11.52 ± 0.05 eV. Experimental findings are fully supported by theoretical calculations at the G4 level of theory (ZPVE corrected energies at 0 K), giving a value of 11.33 eV for the adiabatic ionization energy of butanenitrile and an exothermicity of 0.49 for fragmentation into [CH2CNH](•+) plus C2H4, hampered by an energy barrier of 0.29 eV. The energy difference between [CH3CN](•+) and [CH2CNH](•+) is 2.28 eV (with the latter being the lowest energy isomer), and the isomerization barrier is 0.84 eV. Reactive monitoring experiments of the [CH3CN](•+) and [CH2CNH](•+) isomers with C2H4 have been performed using the CERISES guided ion beam tandem mass spectrometer and exploiting the selectivity of ethylene that gives exothermic charge exchange and proton transfer reactions with [CH3CN](•+) but not with [CH2CNH](•+) isomers. In addition, minor reactive channels are observed leading to the formation of new C-C bonds upon reaction of [CH3CN](•+) with C2H4, and their astrochemical implications are briefly discussed.
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 2155/3, 18223 Prague 8, Czech Republic.
authors.forename: Miroslav
authors.initials: M
authors.lastname: Polášek
authors.affiliation: Sorbonne Universités, UPMC Univ. Paris 06, MONARIS, UMR 8233, Université Pierre et Marie Curie , 4 Place Jussieu, case courrier 49, F-75252 Paris Cedex 05, France.
authors.forename: Emilie-Laure
authors.initials: EL
authors.lastname: Zins
authors.affiliation: Laboratoire de Chimie Physique, Bât. 350, UMR 8000, CNRS-Univ. Paris-Sud & Paris-Saclay , Centre Universitaire Paris-Sud, 91405 Orsay Cedex, France.|Synchrotron SOLEIL , L'Orme des Merisiers, Saint-Aubin - BP 48, 91192 Gif-sur-Yvette, France.
authors.forename: Christian
authors.initials: C
authors.lastname: Alcaraz
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 2155/3, 18223 Prague 8, Czech Republic.
authors.forename: Ján
authors.initials: J
authors.lastname: Žabka
authors.affiliation: J. Heyrovský Institute of Physical Chemistry, Academy of Sciences of the Czech Republic , Dolejškova 2155/3, 18223 Prague 8, Czech Republic.
authors.forename: Věra
authors.initials: V
authors.lastname: Křížová
authors.affiliation: Department of Physics, University of Trento , Via Sommarive 14, 38123 Povo, Italy.
authors.forename: Linda
authors.initials: L
authors.lastname: Giacomozzi
authors.affiliation: Department of Physics, University of Trento , Via Sommarive 14, 38123 Povo, Italy.
authors.forename: Paolo
authors.initials: P
authors.lastname: Tosi
authors.affiliation: Department of Physics, University of Trento , Via Sommarive 14, 38123 Povo, Italy.
authors.forename: Daniela
authors.initials: D
authors.lastname: Ascenzi