Positive and negative ions of the amino acid histidine formed in low-energy electron collisions.

Histidine is an aromatic amino acid crucial for the biological functioning of proteins and enzymes. When biological matter is exposed to ionising radiation, highly energetic particles interact with the surrounding tissue which leads to efficient formation of low-energy electrons. In the present study, the interaction of low-energy electrons with gas-phase histidine is studied at a molecular level in order to extend the knowledge of electron-induced reactions with amino acids.

The adsorption of helium atoms on small cationic gold clusters.

Adducts formed between small gold cluster cations and helium atoms are reported for the first time. These binary ions, Aun+Hem, were produced by electron ionization of helium nanodroplets doped with neutral gold clusters and were detected using mass spectrometry. For a given value of n, the distribution of ions as a function of the number of added helium atoms, m, has been recorded.

Isomeric Broadening of C Electronic Excitation in Helium Droplets: Experiments Meet Theory.

Helium is considered an almost ideal tagging atom for cold messenger spectroscopy experiments. Although helium is bound very weakly to the ionic molecule of interest, helium tags can lead to shifts and broadenings that we recorded near 963.5 nm in the electronic excitation spectrum of C solvated with up to 100 helium atoms.

The structure of coronene cluster ions inferred from H uptake in the gas phase.

Mass spectra of helium nanodroplets doped with H and coronene feature anomalies in the ion abundance that reveal anomalies in the energetics of adsorption sites. The coronene monomer ion strongly adsorbs up to n = 38 H molecules indicating a commensurate solvation shell that preserves the D symmetry of the substrate. No such feature is seen in the abundance of the coronene dimer through tetramer complexed with H; this observation rules out a vertical columnar structure.

Atomically resolved phase transition of fullerene cations solvated in helium droplets.

Helium has a unique phase diagram and below 25 bar it does not form a solid even at the lowest temperatures. Electrostriction leads to the formation of a solid layer of helium around charged impurities at much lower pressures in liquid and superfluid helium. These so-called 'Atkins snowballs' have been investigated for several simple ions.