[en] Copper nanoparticles are promising, low-cost candidates for the catalytic splitting of water and production of hydrogen gas. The present gas-phase study, based on the synthesis of copper-water complexes in ultracold helium nanodroplets followed by electron ionization, attempts to find evidence for dissociative water adsorption and H₂ formation. Mass spectra show that H₂O–Cu complexes containing dozens of copper and water molecules can be formed in the helium droplets. However, ions that would signal the production and escape of H₂, such as (H₂O)_n−2(OH)₂Cu_m⁺ or the isobaric (H₂O)_n−1OCu_m⁺, could not be detected. We do observe an interesting anomaly though: While the abundance of stoichiometric (H₂O)_nCu_m⁺ ions generally exceeds that of protonated or dehydrogenated ions, the trend is reversed for (H₂O)OHCu₂⁺ and (H₂O)₂OHCu₂⁺; these ions are more abundant than (H₂O)₂Cu₂⁺ and (H₂O)₃Cu₂⁺, respectively. Moreover, (H₂O)₂OHCu₂⁺ is much more abundant than other ions in the (H₂O)_n−1OHCu₂⁺ series. A byproduct of our experiment is the observation of enhanced stability of He₆Cu⁺, He₁₂Cu⁺, He₂₄Cu⁺, and He₂Cu₂⁺. Graphical abstract: .

[en] Highlights: • Electron emission upon Ar⁺ surface impact was studied with sub-mm spatial resolution. • The current density and energy of Ar⁺ is comparable to DC magnetron sputtering. • The influence of the grain orientation and surface contaminations was studied. • Crystal orientation has no influence on the ion induced electron emission yield. The ion induced electron emission yield upon Ar⁺ ion impact at 420 eV was measured for a stainless-steel sample that was partially covered with a 50 nm thick gold layer. The ion induced electron emission yield for the two target materials differs strongly and enables to reproduce the shape of the gold film with a spatial resolution that corresponds to the width of the ion beam, which is 240 µm in the present case. Details in the two-dimensional map of the ion induced electron emission yield are explained by comparison with optical and scanning electron microscopy as well as with X-ray photoelectron spectroscopy measurements of the sample surface. In contrast to the sputtering efficiency, the ion induced electron emission yield does not depend on the orientation of the crystal structure.

[en] 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. Graphical abstract: .