Electron-induced chemistry in imidazole clusters embedded in helium nanodroplets

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.

29 pages, 10 figures