Trihydrogen Cation Helium Clusters: A New Potential Energy Surface.

We present a new analytical potential energy surface (PES) for the interaction between the trihydrogen cation and a He atom, , in its electronic ground state. The proposed PES has been built as a sum of two contributions: a polarization energy term due to the electric field generated by the molecular cation at the position of the polarizable He atom, and an exchange-repulsion and dispersion interactions represented by a sum of "atom-bond" potentials between the three bonds of and the He atom. All parameters of this new PES have been chosen and fitted from data obtained from high-level ab-initio calculations.

Correction: Helium nanodroplets as an efficient tool to investigate hydrogen attachment to alkali cations.

Correction for 'Helium nanodroplets as an efficient tool to investigate hydrogen attachment to alkali cations' by Siegfried Kollotzek , , 2023, , 462-470, https://doi.org/10.1039/D2CP03841B.

Observation of Multiple Ordered Solvation Shells in Doped Helium Droplets: The Case of HeCa.

In this Letter, we report the experimental detection of likely the largest ordered structure of helium atoms surrounding a monatomic impurity observed to date using a recently developed technique. The mass spectrometry investigation of HeCa clusters, formed in multiply charged helium nanodroplets, reveals magic numbers at = 12, 32, 44, and 74. Classical optimization and path integral Monte Carlo calculations suggest the existence of up to four shells surrounding the calcium dication which are closed with well-ordered Mozartkugel-like structures: HeCa with an icosahedron, the second at HeCa with a dodecahedron, the third at HeCa with a larger icosahedron, and finally for HeCa, we find that the outermost He atoms form an icosidodecahedron which contains the other inner shells.

Helium nanodroplets as an efficient tool to investigate hydrogen attachment to alkali cations.

We report a novel method to reversibly attach and detach hydrogen molecules to positively charged sodium clusters formed inside a helium nanodroplet host matrix. It is based on the controlled production of multiply charged helium droplets which, after picking up sodium atoms and exposure to H vapor, lead to the formation of Na(H) clusters, whose population was accurately measured using a time-of-flight mass spectrometer. The mass spectra reveal particularly favorable Na(H) and Na(H) clusters for specific "magic" numbers of attached hydrogen molecules.

Ca Ions Solvated in Helium Clusters.

We present a combined experimental and theoretical investigation on Ca+ ions in helium droplets, HeNCa+. The clusters have been formed in the laboratory by means of electron-impact ionization of Ca-doped helium nanodroplets. Energies and structures of such complexes have been computed using various approaches such as path integral Monte Carlo, diffusion Monte Carlo and basin-hopping methods.

Snowball formation for Cs solvation in molecular hydrogen and deuterium.

Interactions of atomic cations with molecular hydrogen are of interest for a wide range of applications in hydrogen technologies. These interactions are fairly strong despite being non-covalent, hence one can ask whether hydrogen molecules would form dense, solid-like, solvation shells around the ion (snowballs) or rather a more weakly bound compound. In this work, the interactions between Cs+ and H2 are studied both experimentally and computationally.

A combined experimental and theoretical investigation of Cs ions solvated in He clusters.

Solvation of Cs ions inside helium droplets has been investigated both experimentally and theoretically. On the one hand, mass spectra of doped helium clusters ionized with a crossed electron beam, HeCs, have been recorded for sizes up to N = 60. The analysis of the ratio between the observed peaks for each size N reveals evidences of the closure of the first solvation shell when 17 He atoms surround the alkali ion.

Lithium ions solvated in helium.

We report on a combined experimental and theoretical study of Li+ ions solvated by up to 50 He atoms. The experiments show clear enhanced abundances associated with HenLi+ clusters where n = 2, 6, 8, and 14. We find that classical methods, e.

Adsorption of molecular hydrogen on coronene with a new potential energy surface.

Benchmark interaction energies between coronene, CH, and molecular hydrogen, H, have been computed by means of high level electronic structure calculations. Binding energies, equilibrium distances and strengths of the long range attraction, evaluated for the basic configurations of the H-CH complex, indicate that the system is not too affected by the relative orientations of the diatom, suggesting that its behavior can be approximated to that of a pseudoatom. The obtained energy profiles have confirmed the noncovalent nature of the bonding and serve to tune-up the parameters of a new force field based on the atom-bond approach which correctly describes the main features of the H-coronene interaction.

Comparative investigation of pure and mixed rare gas atoms on coronene molecules.

Clusters formed by the combination of rare gas (RG) atoms of He, Ne, Ar, and Kr on coronene have been investigated by means of a basin-hopping algorithm and path integral Monte Carlo calculations at T = 2 K. Energies and geometries have been obtained and the role played by the specific RG-RG and RG-coronene interactions on the final results is analysed in detail. Signatures of diffuse behavior of the He atoms on the surface of the coronene are in contrast with the localization of the heavier species, Ar and Kr.

Examination of the Feynman-Hibbs Approach in the Study of NeN-Coronene Clusters at Low Temperatures.

Feynman-Hibbs (FH) effective potentials constitute an appealing approach for investigations of many-body systems at thermal equilibrium since they allow us to easily include quantum corrections within standard classical simulations. In this work we apply the FH formulation to the study of NeN-coronene clusters (N = 1-4, 14) in the 2-14 K temperature range. Quadratic (FH2) and quartic (FH4) contributions to the effective potentials are built upon Ne-Ne and Ne-coronene analytical potentials.

Coronene molecules in helium clusters: Quantum and classical studies of energies and configurations.

Coronene-doped helium clusters have been studied by means of classical and quantum mechanical (QM) methods using a recently developed He-C24H12 global potential based on the use of optimized atom-bond improved Lennard-Jones functions. Equilibrium energies and geometries at global and local minima for systems with up to 69 He atoms were calculated by means of an evolutive algorithm and a basin-hopping approach and compared with results from path integral Monte Carlo (PIMC) calculations at 2 K. A detailed analysis performed for the smallest sizes shows that the precise localization of the He atoms forming the first solvation layer over the molecular substrate is affected by differences between relative potential minima.

[Bacteremia due to Pasteurella spp.: a rare process in our hospital over the last 8 years].

Objectives: To review and update the epidemic and clinical knowledge concerning disseminated blood disease caused by Pasteurella species in our area.

Methods: Retrospective study of Pasteurella species bacteremia (PSB) episodes occurring in patients attended from January 1994 to December 2001 in a single tertiary hospital.

Results: Among the 31 clinical samples remitted to the Microbiology Laboratory in which a species of Pasteurella was identified, 5 (16%) corresponded to positive blood cultures in 5 patients.