Johannes Postler

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium

The Virtual Atomic and Molecular Data Centre (VAMDC) Consortium is a worldwide consortium which federates atomic and molecular databases through an e-science infrastructure and an organisation to support this activity. About 90% of the inter-connected databases handle data that are used for the interpretation of astronomical spectra and for modelling in many fields of astrophysics. Recently the VAMDC Consortium has connected databases from the radiation damage and the plasma communities, as well as promoting the publication of data from Indian institutes. This paper describes how the VAMDC Consortium is organised for the optimal distribution of atomic and molecular data for scientific research. It is noted that the VAMDC Consortium strongly advocates that authors of research papers using data cite the original experimental and theoretical papers as well as the relevant databases.

Detection of Negative Charge Carriers in Superfluid Helium Droplets: The Metastable Anions He* − and He 2 * −

Helium droplets provide the possibility to study phenomena at the very low temperatures at which quantum mechanical effects are more pronounced and fewer quantum states have significant occupation probabilities. Understanding the migration of either positive or negative charges in liquid helium is essential to comprehend charge-induced processes in molecular systems embedded in helium droplets. Here, we report the resonant formation of excited metastable atomic and molecular helium anions in superfluid helium droplets upon electron impact. Although the molecular anion is heliophobic and migrates toward the surface of the helium droplet, the excited metastable atomic helium anion is bound within the helium droplet and exhibits high mobility. The atomic anion is shown to be responsible for the formation of molecular dopant anions upon charge transfer and thus, we clarify the nature of the previously unidentified fast exotic negative charge carrier found in bulk liquid helium.

Electron interaction with nitromethane embedded in helium droplets: Attachment and ionization measurements

Results of a detailed study on electron interactions with nitromethane (CH(3)NO(2)) embedded in helium nanodroplets are reported. Anionic and cationic products formed are analysed by mass spectrometry. When the doped helium droplets are irradiated with low-energy electrons of about 2 eV kinetic energy, exclusively parent cluster anions (CH(3)NO(2))(n)(-) are formed. At 8.5 eV, three anion cluster series are observed, i.e., (CH(3)NO(2))(n)(-), [(CH(3)NO(2))(n)-H](-), and (CH(3)NO(2))(n)NO(2)(-), the latter being the most abundant. The results obtained for anions are compared with previous electron attachment studies with bare nitromethane and nitromethane condensed on a surface. The cation chemistry (induced by electron ionization of the helium matrix at 70 eV and subsequent charge transfer from He(+) to the dopant cluster) is dominated by production of methylated and protonated nitromethane clusters, (CH(3)NO(2))(n)CH(3)(+) and (CH(3)NO(2))(n)H(+).

Formation of Dianions in Helium Nanodroplets

The formation of dianions in helium nanodroplets is reported for the first time. The fullerene cluster dianions (C60)n(2-) and (C70)n(2-) were observed by mass spectrometry for n≥5 when helium droplets containing the appropriate fullerene were subjected to electron impact at approximately 22 eV. A new mechanism for dianion formation is described, which involves a two-electron transfer from the metastable He(-) ion. As well as the prospect of studying other dianions at low temperature using helium nanodroplets, this work opens up the possibility of a wider investigation of the chemistry of He(-), a new electron-donating reagent.

Electron attachment to CO2 embedded in superfluid He droplets.

Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2)n– and (CO2)nO– and, at much lower intensities, He containing ions of the form Hem(CO2)nO–. At low energies (<5 eV), predominantly the non-decomposed complexes (CO2)n– are formed via two resonance contributions, similar to electron attachment to pristine CO2 clusters. The significantly different shapes and relative resonance positions, however, indicate particular quenching and mediation processes in CO2@He. A series of further resonances in the energy range up to 67 eV can be assigned to electronic excitation of He and capture of the inelastically scattered electron generating (CO2)n– and two additional processes where an intermediately formed He* leads to the nonstoichiometric anions (CO2)nO–.

Electron Attachment to CO2 Embedded in Superfluid He Droplets

Electron attachment to CO2 embedded in superfluid He droplets leads to ionic complexes of the form (CO2)n– and (CO2)nO– and, at much lower intensities, He containing ions of the form Hem(CO2)nO–. At low energies (<5 eV), predominantly the non-decomposed complexes (CO2)n– are formed via two resonance contributions, similar to electron attachment to pristine CO2 clusters. The significantly different shapes and relative resonance positions, however, indicate particular quenching and mediation processes in CO2@He. A series of further resonances in the energy range up to 67 eV can be assigned to electronic excitation of He and capture of the inelastically scattered electron generating (CO2)n– and two additional processes where an intermediately formed He* leads to the nonstoichiometric anions (CO2)nO–.

C-60(+) and the Diffuse Interstellar Bands: An Independent Laboratory Check

In 2015, Campbell et al. presented spectroscopic laboratory gas phase data for the fullerene cation,

Radiation damage of biomolecules (RADAM) database development: current status

{{{\rm{C}}}_{60}}^{+}

Electron-Induced Chemistry of Cobalt Tricarbonyl Nitrosyl (Co(CO)3NO) in Liquid Helium Nanodroplets.

, that coincide with the reported astronomical spectra of two diffuse interstellar band (DIB) features at 9633 and 9578 A. In the following year, additional laboratory spectra were linked to three other and weaker DIBs at 9428, 9366, and 9349 A. The laboratory data were obtained using wavelength-dependent photodissociation spectroscopy of small (up to three) He-tagged

Isomeric Broadening of C60+ Electronic Excitation in Helium Droplets: Experiments Meet Theory

{{{\rm{C}}}_{60}}^{+}\mbox{--}{\mathrm{He}}_{n}