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PubMed | Institute Fsica Fundamental and University of Innsbruck
Type: Journal Article | Journal: The journal of physical chemistry. A | Year: 2015

We present variational calculations on systems containing a few boson helium atoms attached to electronically excited atomic and molecular helium anions He* and He* and characterize their structures and energetics. Previously reported high-level ab initio results [Huber, S. E.; Mauracher, A. Mol. Phys. 2014, 112, 794] to describe the interactions between excited (metastable) anions and a neutral He atom have been employed. For the case of the atomic species He*, the corresponding interaction with He suggests large anharmonicity effects due to the presence of a deep well of 17,500 cm at short distances, together with a more external shallow secondary well of 4 cm, both supporting bound levels. Moreover, when a sum of pairwise interactions is assumed to describe the full PES corresponding to the presence of several neutral He atoms, geometrical constraints already predict the complete solvation of the anionic impurity by six helium atoms, giving rise to a bipyramidal structure. In turn, for the anisotropic weak interaction He-He*, where the anionic dimer is considered as a rigid rotor, the obtained structures show the tendency of the helium atoms to pack themselves together and largely far away from the dopant, thereby confirming the heliophobic character of He*.

Bulut N.,Firat University | Roncero O.,Institute Fsica Fundamental | Jorfi M.,University of Le Havre | Honvault P.,University of Burgundy
Journal of Chemical Physics | Year: 2011

We present accurate quantum calculations of state-to-state cross sections for the N OH → NO H reaction performed on the ground 3A′′ global adiabatic potential energy surface of Guadagnini [J. Chem. Phys. 102, 774 (1995)10.1063/1.469191. The OH reagent is initially considered in the rovibrational state v 0, j 0 and wave packet calculations have been performed for selected total angular momentum, J 0, 10, 20, 30, 40,120. Converged integral state-to-state cross sections are obtained up to a collision energy of 0.5 eV, considering a maximum number of eight helicity components, = 0.7. Reaction probabilities for J = 0 obtained as a function of collision energy, using the wave packet method, are compared with the recently published time-independent quantum mechanical one. Total reaction cross sections, state-specific rate constants, opacity functions, and product state-resolved integral cross-sections have been obtained by means of the wave packet method for several collision energies and compared with recent quasi-classical trajectory results obtained with the same potential energy surface. The rate constant for OH(v 0, j 0) is in good agreement with the previous theoretical values, but in disagreement with the experimental data, except at 300 K. © 2011 American Institute of Physics. © 2011 American Institute of Physics.

PubMed | Australian National University, Complutense University of Madrid, James Cook University, Flinders University and Institute Fsica Fundamental
Type: Journal Article | Journal: The Journal of chemical physics | Year: 2015

Utilising a high-resolution, trap-based positron beam, we have measured both elastic and inelastic scattering of positrons from water vapour. The measurements comprise differential elastic, total elastic, and total inelastic (not including positronium formation) absolute cross sections. The energy range investigated is from 1 eV to 60 eV. Comparison with theory is made with both R-Matrix and distorted wave calculations, and with our own application of the Independent Atom Model for positron interactions.

Perez-Ros J.,Institute Fsica Fundamental | Tejeda G.,CSIC - Institute for the Structure of Matter | Fernndez J.M.,CSIC - Institute for the Structure of Matter | Hernndez M.I.,Institute Fsica Fundamental | Montero S.,CSIC - Institute for the Structure of Matter
Journal of Chemical Physics | Year: 2011

Close-coupling calculations and experiment are combined in this work, which is aimed at establishing a set of state-to-state rate coefficients for elementary processes ij → m in O2:O2 collisions at low temperature involving the rotational states i, j, , m of the vibrational ground state of 16O2(3g-). First, a set of cross sections for inelastic collisions is calculated as a function of the collision energy at the converged close-coupled level via the MOLSCAT code, using a recent ab-initio potential energy surface for O2-O2 [M. Bartolomei, J. Chem. Phys. 133, 124311 (2010)10.1063/1.3479395]. Then, the corresponding rates for the temperature range 4 T 34 K are derived from the cross sections. The link between theory and experiment is a Master Equation which accounts for the time evolution of rotational populations in a reference volume of gas in terms of the collision rates. This Master Equation provides a linear function of the rates for each rotational state and temperature. In the experiment, the evolution of rotational populations is measured by Raman spectroscopy in a tiny reference volume (≈2 10-4 mm3) of O2 travelling along the axis of a supersonic jet at a velocity of ≈700 m/s. The accuracy of the calculated rates is assessed experimentally for 10 T 34 K by means of the Master Equation. The rates, jointly with their confidence interval estimated by Monte Carlo simulation, account to within the experimental uncertainty for the evolution of the populations of the N 1, 3, 5, 7 rotational triads along the supersonic jet. Confidence intervals range from ≈6 for the dominant rates at 34 K, up to ≈17 at 10 K. These results provide an experimental validation of state-to-state rates for O2:O2 inelastic collisions calculated in the close-coupling approach and, indirectly, of the anisotropy of the O2-O2 intermolecular potential employed in the calculation for energies up to 300 cm-1. © 2011 American Institute of Physics.

Porez-Ros J.,Institute Fsica Fundamental | Campos-Martnez J.,Institute Fsica Fundamental | Hernndez M.I.,Institute Fsica Fundamental
Journal of Chemical Physics | Year: 2011

The collision dynamics of 17O2(3g-) +17O2(3g-) in the presence of a magnetic field is studied within the close-coupling formalism in the range between 10 nK and 50mK. A recent global ab initio potential energy surface (PES) is employed and its effect on the dynamics is analyzed and compared with previous calculations where an experimentally derived PES was used [T. V. Tscherbul, New J. Phys 134, 055021 (2009)]. Compared to the results using the older PES, magnetic-field dependence of the low-field-seeking state in the ultracold regime is characterized by a very large background scattering length, abg, and cross sections exhibit broader and more pronounced Feshbach resonances. The marked resonance structure is somewhat surprising considering the influence of inelastic scattering but it can be explained by resorting to the analytical van der Waals theory, where the short-range amplitude of the entrance channel wavefunction is enhanced by the large abg. This strong sensitivity to the short range of the ab initio PES persists up to relatively high energies (10mK). After this study and despite quantitative predictions are very difficult, it can be concluded that the ratio between elastic and spin relaxation scattering is generally small, except for magnetic fields which are either low or close to an asymmetric Fano-type resonance. Some general trends found here, such as a large density of quasibound states and a propensity toward large scattering lengths, could be also characteristic of other anisotropic molecule-molecule systems. © 2011 American Institute of Physics.

Lange E.,New University of Lisbon | Meneses G.,New University of Lisbon | Cunha T.,New University of Lisbon | Krasuska J.,Siedlce University Of Natural Sciences And Humanities | And 4 more authors.
Journal of Physics: Conference Series | Year: 2015

Here we present negative ion formation driven by electron transfer in atom (potassium) molecule collision and dissociative electron attachment in sulphur containing compounds, probing the influence of sulphur atoms in the decomposition mechanism of two biological relevant molecules: thiaproline and taurine. © Published under licence by IOP Publishing Ltd.

PubMed | University of Perugia, Institute Fsica Fundamental and University of Tokyo
Type: Journal Article | Journal: The journal of physical chemistry letters | Year: 2015

Graphynes are novel two-dimensional carbon-based materials that have been proposed as molecular filters, especially for water purification technologies. We carry out first-principles electronic structure calculations at the MP2C level of theory to assess the interaction between water and graphyne, graphdiyne, and graphtriyne pores. The computed penetration barriers suggest that water transport is unfeasible through graphyne while being unimpeded for graphtriyne. For graphdiyne, with a pore size almost matching that of water, a low barrier is found that in turn disappears if an active hydrogen bond with an additional water molecule on the opposite side of the opening is considered. Thus, in contrast with previous determinations, our results do not exclude graphdiyne as a promising membrane for water filtration. In fact, present calculations lead to water permeation probabilities that are 2 orders of magnitude larger than estimations based on common force fields. A new pair potential for the water-carbon noncovalent component of the interaction is proposed for molecular dynamics simulations involving graphdiyne and water.

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