A high sensitivity, high resolution tandem mass spectrometer to research low-energy, reactive ion-surface interactions Review of Scientific Instruments 91, 065101 (2020);

Ionic complexes between gold and C60 have been observed for the first time. Cations and anions of the type [Au(C60)2]+/– are shown to have particular stability. Calculations suggest that these ions adopt a C60–Au–C60 sandwich-like (dumbbell) structure, which is reminiscent of [XAuX]+/– ions previously observed for much smaller ligands. The [Au(C60)2]+/– ions can be regarded as Au(I) complexes, regardless of whether the net charge is positive or negative, but in both cases, the charge transfer between the Au and C60 is incomplete, most likely because of a covalent contribution to the Au–C60 binding. The C60–Au–C60 dumbbell structure represents a new architecture in fullerene chemistry that might be replicable in synthetic nanostructures.

High-resolution mass spectra of helium droplets doped with gold and ionized by electrons reveal He n Au+ cluster ions. Additional doping with heavy noble gases results in Ne n Au+, Ar n Au+, Kr n Au+, and Xe n Au+ cluster ions. The high stability predicted for covalently bonded Ar2Au+, Kr2Au+, and Xe2Au+ is reflected in their relatively high abundance. Surprisingly, the abundance of Ne2Au+, which is predicted to have zero covalent bonding character and no enhanced stability, features a local maximum, too. The predicted size and structure of complete solvation shells surrounding ions with essentially nondirectional bonding depends primarily on the ratio σ* of the ion–ligand versus the ligand–ligand distance. For Au+ solvated in helium and neon, the ratio σ* is slightly below 1, favoring icosahedral packing in agreement with a maximum observed in the corresponding abundance distributions at n = 12. He n Au+ appears to adopt two additional solvation shells of I h symmetry, containing 20 and 12 atoms, respectively. For Ar n Au+, with σ* ≈ 0.67, one would expect a solvation shell of octahedral symmetry, in agreement with an enhanced ion abundance at n = 6. Another anomaly in the ion abundance at Ar9Au+ matches a local maximum in its computed dissociation energy.

Helium nanodroplets are doped with cesium and molecular hydrogen and subsequently ionized by electrons. Mass spectra reveal HxCs + ions that contain as many as 130 hydrogen atoms. Two features in the spectra are striking: First, the abundance of ions with an odd number of hydrogen atoms is very low; the abundance of HCs + is only 1 % that of H2Cs + . The dominance of even-numbered species is in stark contrast to previous studies of pure or doped hydrogen cluster ions. Second, the abundance of (H2)nCs + features anomalies at n = 8, 12, 32, 44, and 52. Guided by previous work on ions solvated in hydrogen and helium we assign the anomalies at n = 12, 32, 44 to the formation of three concentric, solid-like solvation shells of icosahedral symmetry around Cs + . Preliminary density functional theory calculations for n  14 are reported as well.

Two different types of experiments were performed. In the first experiment we studied the low-temperature condensation of vaporized graphite inside bulk liquid helium while in the second experiment the condensation of single carbon atoms together with H2, H2O, and CO molecules inside helium nanodroplets was studied. The condensation of vaporized graphite leads to the formation of partially graphitized carbon, which indicates high-temperatures, supposedly higher than 1000 °C, during the condensation. Possible underlying processes responsible for the instant rise in temperature during condensation are discussed. This suggests that such processes cause the presence of partially graphitized carbon dust formed by low-temperatures condensation in the diffuse interstellar medium. Alternatively, in the denser regions of the ISM, the condensation of carbon atoms together with the most abundant interstellar molecules (H2, H2O, and CO), leads to the formation of complex organic molecules (COMs) and finally organic polymers.Water molecules were found not to be involved directly in the reaction network leading to the formation of COMs. It was proposed that COMs are formed via addition of carbon atoms to H2 and CO molecules (C + H2 → HCH, HCH + CO → OCCH2). Due to the involvement of molecular hydrogen, the formation of COMs by carbon addition reactions should be more efficient at high extinctions compared with the previously proposed reaction scheme with atomic hydrogen.