Regular Article

Electron-induced chemistry in imidazole clusters embedded in helium nanodroplets^★

¹ Institut für Ionenphysik und Angewandte Physik, Universität Innsbruck, Technikerstraße 25, 6020 Innsbruck, Austria
² Department of Physics, Karaj Branch, Islamic Azad University, Karaj, Iran
³ Université de Lyon, Université Claude Bernard Lyon1, CNRS/IN2P3, UMR5822, Institut de Physique Nucléaire de Lyon, 43 Bd du 11 novembre 1918, 69622 Villeurbanne, France

^a e-mail: l.feketeova@ipnl.in2p3.fr

Received: 30 September 2017
Received in final form: 14 November 2017
Published online: 8 February 2018

Abstract

Electron-induced chemistry in imidazole (IMI) clusters embedded in helium nanodroplets (with an average size of 2 × 10⁵ He atoms) has been investigated with high-resolution time-of-flight mass spectrometry. The formation of both, negative and positive, ions was monitored as a function of the cluster size n. In both ion spectra a clear series of peaks with IMI cluster sizes up to at least 25 are observed. While the anions are formed by collisions of IMI_n with He^*–, the cations are formed through ionization of IMI_n by He⁺ as the measured onset for the cation formation is observed at 24.6 eV (ionization energy of He). The most abundant series of anions are dehydrogenated anions IMI_n–1(IMI–H)^–, while other anion series are IMI clusters involving CN and C₂H₄ moieties. The formation of cations is dominated by the protonated cluster ions IMI_nH⁺, while the intensity of parent cluster cations IMIn⁺ is also observed preferentially for the small cluster size n. The observation of series of cluster cations [IMI_nCH₃]⁺ suggests either CH3⁺ cation to be solvated by n neutral IMI molecules, or the electron-induced chemistry has led to the formation of protonated methyl-imidazole solvated by (n – 1) neutral IMI molecules.