Graphdiyne based membranes: exceptional performances for helium separation applications

Graphdiyne is a novel two-dimensional material deriving from graphene that has been recently synthesized and featuring uniformly distributed sub-nanometer pores. We report accurate calculations showing that graphdiyne pores permit an almost unimpeded helium transport which can be used for its chemical and isotopic separation. Exceptionally high He/CH_4 selectivities are found which largely exceed the performance of the best membranes used to date for extraction from natural gas. Moreover, by exploiting slight differences in the tunneling probabilities of ^3He and ^4He, we also find promising results for the separation of the Fermionic isotope at low temperature

Transmission of Helium through Graphynes Pores: First Principles Calculations and Quantum Mechanical Simulations

AMOC 2015, Anharmonicity in médium-sized molecules and cluster, CSIC, Madrid (Spain), 26-30 April 2015; http://tct1.iem.csic.es/AMOC2015.htmPeer Reviewe

Laboratory study of rate coefficients for H2O:He inelastic collisions between 20 and 120K

8 pags. ; 7 figs. ; 4 tabls. ; Supporting material: machine-readable tablesState-to-state rate coefficients for ortho-H2O:He and para-H2O:He inelastic collisions in the 20-120 K thermal range are investigated by means of an improved experimental procedure. This procedure is based on the use of a kinetic master equation (MEQ) which describes the evolution of populations of H2O rotational levels along a supersonic jet of H2O highly diluted in helium. The MEQ is expressed in terms of experimental observables and rate coefficients for H2O:He inelastic collisions. The primary experimental observables are the local number density and the populations of the rotational energy levels of H2O, quantities which are determined along the jet with unprecedented accuracy by means of Raman spectroscopy with high space resolution. Sets of rate coefficients from the literature and from present close-coupling calculations using two different potential energy surfaces (PESs) have been tested against the experiment. The Green et al. rate coefficients are up to 50% too low compared to the experiment, while most rates calculated here from the Hodges et al. PES and the Patkowski et al. PES are much closer to the experimental values. Experimental rates with an estimated accuracy on the order of 10% have been obtained for ortho-H2O:He and para-H2O:He inelastic collisions between 20 and 120 K by scaling and averaging the theoretical rates to the experiment. 2015. C The American Astronomical SocietyThis work has been supported by the Spanish Ministerios de Innovación (MICINN) and Economía y Competitividad (MINECO) through the research projects FIS2010-22064-C01, FIS2010-22064-C02, FIS2013-48275-C2-1-P, and FIS2013-48275-C2-2-P, and CONSOLIDER-ASTROMOL CSD2009-0038.Peer reviewe

The Molecular Oxygen Tetramer: Intermolecular Interactions and Implications for the ϵ\epsilon Solid Phase

Recent data have determined that the structure of the high pressure $\epsilon$ phase of solid oxygen consists of clusters composed of four O$_2$ molecules. This finding has opened the question about the nature of the intermolecular interactions within the molecular oxygen tetramer. We use multiconfigurational ab initio calculations to obtain an adequate characterization of the ground singlet state of (O$_2$)$_4$ which is compatible with the non magnetic character of the $\epsilon$ phase. In contrast to previous suggestions implying chemical bonding, we show that (O$_2$)$_4$ is a van der Waals like cluster where exchange interactions preferentially stabilize the singlet state. However, as the cluster shrinks, there is an extra stabilization due to many-body interactions that yields a significant softening of the repulsive wall. We show that this short range behavior is a key issue for the understanding of the structure of $\epsilon$-oxygen

Interactions in Oxygen: from the gas to high pressure solid phases

7th International Meeting on Photodynamics, Maresias SP, Brazil, 14-20 Oct. 2012Peer Reviewe

Erratum: Molecular oxygen tetramer (O2)4: Intermolecular interactions and implications for the ε solid phase

1 págs.; 1 fig.; PACS number(s): 36.40.−c, 31.15.ae, 34.20.Gj, 62.50.−p, 99.10.CdErratum to: (Physical Review B - Condensed Matter and Materials Physics (2011) 84 (092105)Peer Reviewe

Global potential energy surface for the O2 + N2 interaction. Applications to the collisional, spectroscopic, and thermodynamic properties of the complex

A detailed characterization of the interaction between the most abundant molecules in air is important for the understanding of a variety of phenomena in atmospherical science. A completely {\em ab initio} global potential energy surface (PES) for the O$_2(^3\Sigma^-_g)$ + N$_2(^1\Sigma^+_g)$ interaction is reported for the first time. It has been obtained with the symmetry-adapted perturbation theory utilizing a density functional description of monomers [SAPT(DFT)] extended to treat the interaction involving high-spin open-shell complexes. The computed interaction energies of the complex are in a good agreement with those obtained by using the spin-restricted coupled cluster methodology with singles, doubles and noniterative triple excitations [RCCSD(T)]. A spherical harmonics expansion containing a large number of terms due to the anisotropy of the interaction has been built from the {\em ab initio} data. The radial coefficients of the expansion are matched in the long range with the analytical functions based on the recent {\em ab initio} calculations of the electric properties of the monomers [M. Bartolomei et al., J. Comp. Chem., {\bf 32}, 279 (2011)]. The PES is tested against the second virial coefficient $B(T)$ data and the integral cross sections measured with rotationally hot effusive beams, leading in both cases to a very good agreement. The first bound states of the complex have been computed and relevant spectroscopic features of the interacting complex are reported. A comparison with a previous experimentally derived PES is also provided

Aplicación de métodos cuánticos dependientes del tiempo a procesos dinámicos moleculares

Tesis doctoral inédita leída en la Universidad Autónoma de Madrid, Facultad de Ciencias, Departamento de Química Física Aplicada. Fecha de lectura: 22-12-199

Novel nano-porous graphites for gas storage and release

ESPA2016, Castellón de la Plana, Castellón, Spain, June 28, 2016 – July 1, 2016Pristine graphene is in principle an ideal adsorbing material due to its large specific area, stability, mechanical properties and low weight. Nevertheless, the physisorption of light gas species on graphene is in general not particularly favourable, being the adsorption energy, mainly determined by van der Waals interactions, not large enough to guarantee significant storage capacities at standard temperature and pressure. Intercalation between graphene layers could lead to more encouraging adsorption energies but, unfortunately, in pure graphite there is no room for any atomic or molecular species to be hosted. A possible solution to this problem is the use of porous derivative of graphene as ¿building blocks¿ to construct a new class of porous graphites characterized by a larger interlayer volume available for gas storage. To this regard graphynes, which are novel two-dimensional (2D) carbon-based materials, represent promising candidates since they naturally exhibit a nanoweb-like structure characterized by triangular and regularly distributed subnanometer pores[1]. These intriguing features make them appealing for molecular filtering as shown by recent theoretical predictions[2]. The possibility to exploit graphynes as ideal media for the reversible storage of light gases is here theoretically investigated. The focus is first on molecular hydrogen (H2) and, by means of computations at the MP2C[3] level of theory, it is found that graphynes are more suited than graphene for gas hosting since they provide larger binding energies at equilibrium distances much closer to the 2D plane. In particular, for graphtriyne a flat minimum located right in the geometric center of the pore is identified. A novel graphite composed of graphtriyne stacked sheets is then proposed[4] and an estimation of its 3D arrangement is obtained at the DFT (plus dispersion corrections) level of theory by considering a periodic model of the involved bilayers. In contrast to pristine graphite, this new carbon material allow both H2 intercalation and out-of-plane diffusion and related binding energies are obtained by means of MP2C computations: they are found to almost double the estimation for the adsorption on graphene and they could lead to high H2 storage capacities exceeding those found to date for carbon nanostructures of different nature. The proposed layered carbon allotrope also show a preferential adsorption of carbon dioxide (CO2) with respect to other major components (N2, H2O) of the earth atmosphere and could be postulated as an efficient medium for CO2 separation and capture.Peer Reviewe