Electron-induced chemistry in imidazole clusters embedded in helium nanodroplets

TL;DR

This study investigates how electron interactions induce chemical reactions in imidazole clusters within helium nanodroplets, revealing specific ion formation pathways and new chemical species through high-resolution mass spectrometry.

Contribution

It provides the first detailed analysis of electron-induced chemistry in imidazole clusters embedded in helium nanodroplets, identifying ion formation mechanisms and new chemical species.

Findings

Formation of both anions and cations observed up to cluster size 25.

Anions mainly formed by collisions with He$^\star$$^{-}$, cations by ionization of IMI.

Detection of protonated and methylated imidazole cluster ions.

Abstract

Electron-induced chemistry in imidazole (IMI) clusters embedded in helium nanodroplets (with an average size of 2$\times$10$^5$ He atoms) has been investigated with high-resoluton 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$^\star$$^{-}$, the cations are formed through ionization of IMI$_n$ by He$^{+}$ as the measured onset for the cation formation is observed at 24.6 eV (ionization energy of He). The most abundant series of anions are dehydrogenated anions IMI$_{n-1}$(IMI-H)$^{-}$, while other anion series are IMI clusters involving CN and C$_2$H$_4$ moieties. The formation of cations is dominated by the protonated cluster ions IMI$_n$H$^{+}$, while the intensity of parent cluster cations IMI$_n$$^{+}$ is also observed preferentially for the small cluster size n. The observation of series of cluster cations [IMI$_n$CH$_3$]$^{+}$ suggests either CH$_3$$^{+}$ 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.