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Nanoscience and Nanotechnology (N&N), Madrid, mayo 17-20, 2022, Deuterium and tritium constitute relevant substances for many scientific and industrial applications. However, they cannot be easily separated from a mixture with H2, the most abundant hydrogen isotope, as standard methods are based on chemical properties, which are similar for isotopes. For this purpose, in this study, we have employed a quantum-mechanical method that takes into account mass-dependent effects. Graphdiyne, a recently synthesized porous derivative of graphene, offers a promising opportunity to enhance these effects, as its subnanometric pores enable a confinement of the hydrogen molecules when travelling through them. In our simulations the molecules have been treated as pseudoatoms and their interaction with the membrane is represented by an improved Lennard-Jones force field. By performing three-dimensional time-dependent wavepacket propagations, we have obtained the transmission probability of each isotope, which in turn has been used to compute the permeances at different temperatures. Finally, we have calculated the selectivity of deuterium and tritium over hydrogen as the quotient of their permeances: It is seen that the selectivities (favoring the heavier isotopes) increase as temperature decreases until reaching a maximum value. The maximum is a result of a compromise between zero point energy and tunnelling effects, which benefit the heavier and lighter species, respectively. These results are promising for efficient deuterium and tritium separation from hydrogen.

Nanoscience and Nanotechnology (N&N), Madrid, mayo 17-20, 2022, Recent discoveries that graphene permeates protons[1] and hydrogen atoms[2] have opened up prospects of new applications in hydrogen technologies, energy storage and conversion, isotope separation, etc. In addition, a great interest has risen for uncovering the microscopic mechanisms underlying such observations. In the presentation, we will address two processes involved in hydrogenated graphene, namely, the permeation or flipping of chemisorbed hydrogen atoms through a graphene layer and the recombination of these atoms (desorption and formation of hydrogen molecules, a reaction that can occur after permeation). With the aim to provide some insight into these processes, we have carried out density functional theory computations using large molecular prototypes of graphene. Firstly, we will discuss a new mechanism for the flipping of chemisorbed hydrogen atoms[3] or protons[4] (see Fig. 1), for which the estimated activation energies are of the order of the experimental findings[1,2]. Secondly, we will report reaction paths and rate coefficients for the recombination of hydrogen and deuterium and analyze the large isotopic substitution effects[5] observed in thermal desorption measurements[6,7]. Finally, some findings about the role of Stone-Wales defects on the studied processes will be outlined. References [1] S. Hu et al, ¿Proton transport through one-atom-thick crystals¿, Nature, 516 (2014) 227. [2] P. Z. Sun et al, ¿Limits on gas impermeability of graphene¿, Nature, 579 (2020) 229 [3] M. Bartolomei et al, ¿Permeation of chemisorbed hydrogen through graphene: a flipping mechanism elucidated¿, Carbon, 178 (2021) 718 [4] M. Bartolomei et al, ¿Graphene multi-protonation: A cooperative mechanism for proton permeation¿, Carbon, 144 (2019) 144, 724. [5] M. A. Valentín-Rodríguez et al, ¿Reaction paths and tunneling effects in the recombination of H2/D2 from graphene nanoflakes¿, in preparation (2022) [6] T. Zecho et al, ¿Adsorption of hydrogen and deuterium atoms on the (0001) graphite surface¿, J. Chem. Phys. 117, 8486 (2002) [7] L. Hornekaer et al, ¿Metastable structures and recombination pathways for atomic hydrogen on the graphite (0001) surface¿, Phys. Rev. Lett., 96 (2006) 156104

XIII Jornadas de jóvenes investigadores en física atómica y molecular (J²IFAM) , Santiago de Compostela, 16 de marzo 2022, Molecular deuterium is a relevant gas for many different purposes in industry and scientific research. Thus, it is crucial to separate it from other substances in a gas mixture, specially its isotopes. Standard methods have proved not to be very efficient for this separation as deuterium and hydrogen have similar chemical properties. In this work we have exploited a theoretical approach based on quantum sieving, which takes advantage of the enhancement of mass-dependent quantum effects in confined spaces. Subnanometric pores of graphdyine (GDY), a porous derivative of graphene, provide such a confined environment. In the simulations H2/D2 molecules have been treated as pseudoatoms and their interaction with the porous membrane has been modelled by a sum of atom-atom improved Lennard-Jones contributions, which have been obtained by exploiting the comparison with accurate ab initio estimations. With the latter, we have performed three-dimensional time-dependent wavepacket propagations, which yield the transmission probabilities of the gas molecules through GDY. These probabilities are used to compute the permeances (thermal flux divided by gas pressure) at different temperatures. The selectivity of deuterium over hydrogen is obtained as a quotient of their permeances. The selectivity increases as the temperature decreases reaching its highest value around 50 K. This is due to the quantization of the energy levels of the transition state at the centre of the pore. Preliminary results indicate that at lower temperatures the selectivity will eventually decrease because of the tunnelling effect favouring hydrogen over deuterium.

CECAM workshop “Modeling dilute matter in ultracold conditions: from quantum structure to dynamics and reactivity”, Grenoble, 17-19 May 2021 Online Meeting (France), This work has the support of the Spanish grant FIS2017-84391-C2-2-P. Allocation of computing time by CESGA is acknowledged.

cecam2021 : Modeling dilute matter under ultracold solvent: from quantum structure to dynamics and reactivity, 17-19 May 2021 Online Meeting (France)

Microscopic-level understanding of the separation mechanism for two-dimensional (2D) membranes is an active area of research due to potential implications of this class of membranes for various technological processes. Helium (He) purification from the natural resources is of particular interest due to the shortfall in its production. In this work, we applied the ring polymer molecular dynamics (RPMD) method to graphdiyne (Gr2) and graphtriyne (Gr3) 2D membranes having variable pore sizes for the separation of He isotopes. We found that the transmission rate through Gr3 is many orders of magnitude greater than Gr2. The selectivity of either isotope at low temperatures is a consequence of a delicate balance between the zero-point energy effect and tunneling of $^4$He and $^3$He. RPMD provides an efficient approach for studying the separation of He isotopes, taking into account quantum effects of light nuclei motions at low temperatures, which classical methods fail to capture.

CMD2020GEFES. 28th joint conference of Condensed Matter Division of the Spanish Royal Physics Society (RSEF-GEFES) and of the European Physical Society (EPS-C Universidad Autónoma de Madrid, Spain) Del 31 de Agosto al 04 de Septiembre de 2020. .- http://www.cmd2020gefes.eu, Graphene layers with carefully tailored nanopores could be useful tools as filters at the molecular level. Not only molecules of different size could be sieved but it might be also possible to use this 2D materials as appropriate filters for isotopic separation. We present first results on separation of 3He/4He on the nanoporous graphene (NPG) structure proposed in Ref

53 pags., 12 figs., 4 tabs. We review the solvation of atomic, molecular or cluster ions in HNDs. After briefly discussing the properties of snowballs in bulk helium we consider experimental conditions for the efficient synthesis of charged, doped HNDs. We show that the cluster ions observed in conventional mass spectrometers originate from fission of highly charged HNDs. The ionization threshold of HNDs doped with alkalis reveals the minimum cluster size required for full immersion. The abundance distributions of He (Formula presented.) X (Formula presented.) ions frequently reveal local anomalies or magic numbers. We demonstrate that the abundance is approximately proportional to the evaporation energy. Observed and calculated magic numbers will be compiled, including data for ions solvated in molecular hydrogen. Alternative methods to forming He (Formula presented.) X (Formula presented.) that do not employ HNDs will be summarized. Electronic excitation spectra of C (Formula presented.) and polycyclic aromatic hydrocarbon ions reveal the properties of the helium adsorption layer in quantitative detail. Next we discuss theoretical efforts to describe the interaction between ions and helium. We close with summarizing the size dependence of physical quantities computed for atomic alkali and alkaline earth cations in helium, such as binding energy, superfluid fraction, structural order, radial density profiles, and the existence of first and higher solvation shells. This work was supported by the Austrian Science Fund FWF (Project Nos. P31149 and P30355), the European Regional Development Fund (EFRE K-Regio FAENOMENAL, Project No. EFRE 2016- 4), the Swedish Research Council (Contract No. 2016-06625), and the MICINN with Grants No. FIS2017-83157-P and FIS2017-84391-C2-2-P

Zaragoza, 15 -19 de julio de 2019, It has been recently found that pristine graphene and some other 2D materials can be permeated by protons and deuterium at room temperature [1,2], following a low barrier (~ 0.8 eV) activated process. Most of the theoretical attempts have found so far, that permeation of the H+ (D+) involves large energy barriers (around 3.5 eV) and therefore they are too high to explain experiments [3]. In previous models it was assumed an isolated proton permeating the 2D membrane. In this work however, we consider protonated graphene at high local coverage and explore the role played by nearby chemisorbed protons in the process. By using density functional theory calculations (DFT) applied to large molecular prototypes for graphene we have found [4] that when various protons are absorbed on carbons belonging to the same hexagonal ring, permeation barrier can be lowered down to 1.0 eV, thus making feasible the permeation of protons through pristine graphene. The proposed insertion mechanism necessarily need to count with the nearby protons and it could be of relevance not only to help in the understanding of the experimental results, but also in many other scenarios of basic and technological interest. References [1] S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair, E. W. Hill,D. W. Boukhvalov, M. I. Katsnelson, R. A. W. Dryfe, et al., Nature 516, 227 (2014). [2] M. Lozada-Hidalgo, S. Hu, O. Marshall, A. Mishchenko, A. N. Grigorenko, R. A. W. Dryfe,B. Radha, I. V. Grigorieva, and A. K. Geim, Science 351, 68 (2016). [3] Kroes et al., Phys. Chem. Chem. Phys. 19, 5813 (2017), Ekayanake et al. J. Phys.Chem C, 1231, 24335 (2017), Shi et al. J. Phys. Chem. Letts. 8, 4354 (2017), Feng et atl, J. Phys.Chem. Lett., 8 , 6009 (2017), Poltavsky et al. J. Chem. Phys., 148, 204707 (2018), Mazzuca et al, J. Chem. Phys., 148, 224301 (2018). [4] M. Bartolomei, M. I. Hernández, J. Campos-Martínez, R. Hernández-Lamoneda, Carbon, 144, 724-730 (2019).

Zaragoza, 15 -19 de julio de 2019, Interactions between molecular hydrogen and cations of metallic atoms are dominated by charge-quadrupole as well as induction forces, hence they are relatively strong despite being non-covalent. Due to these characteristics, one can ask whether hydrogen molecules would form dense, solid-like, solvation shells around the ion. In this work, the interactions between Cs+ and H2/D2 are investigated both experimentally and computationally. On the one hand, helium nanodroplets doped with cesium and hydrogen or deuterium are ionized by electron impact and the (H2/D2)nCs+ (up to n=30) clusters formed are identified by mass spectrometry. On the other hand, a new and accurate potential energy surface is reported and cluster energies and structures are computed by means of classical and quantum-mechanical Monte Carlo calculations. Dependence of the computed evaporation energies with the cluster size, n, is remarkably similar to the behavior of the measured ion abundances. Clusters (H2)12Cs+ and (D 2)12Cs+ stand out for their stability and quasi-rigid icosahedral structures. However, the first solvation shell involves thirteen or fourteen molecules for hydrogenated or deuterated clusters, respectively. It is found that these solvation layers exhibit the typical characteristics of the well-known Atkins snowballs. The role played by three-body induction interactions as well as the rotational degrees of freedom of the molecules is analyzed and it is found that, despite they are important at a quantitative level (10-15%), they become negligible once the first shell is completed.

IMAMPC2019, Madrid, 11 - 14 June, 2019

EPoLM-4 Workshop, CSIC, Madrid, March 4-6 (2019), This work has been initially motivated by the experimental observation that proton permeation through graphene involves a low activation energy (~0.8 eV)[1], a discovery that contrasted with the common belief that this material is completely impermeable to all atoms under ambient conditions. A possible explanation involves the flipping of a chemisorbed proton from one to the other side of the graphene layer but the related energy barrier is too high (3.5 eV). In this work[2] we have found that this barrier can decrease to the 1.0-1.5 eV range if graphene is assumed to be initially protonated at high local coverage. For this purpose, DFT (PBE/cc-pVTZ) calculations were conducted (exploiting circumcoronene and circumcircumcoronene as graphene prototypes) for an increasing number of protons chemisorbed along a given carbon ring. As seen in Fig.1 (for a five-times protonated carbon ring), the proposed permeation mechanism involves the insertion of the flipping proton into the middle of an effectively broken C-C bond, a linkage that is restored in the products configuration, in analogy with processes originally reported for carbon nanotubes[3]. We believe that these findings can help to rationalize the proton permeation observations since, despite progress[4], theoretical insight is not complete or satisfactory yet. In addition, they can provide clues about properties of hydrogenated graphene as well as about astrochemical processes involving hydrogen and large PAHs[5]. To this end, preliminary results on related processes involving neutral atomic hydrogen will be also reported. [1] S. Hu, M. Lozada-Hidalgo, F. C. Wang, A. Mishchenko, F. Schedin, R. R. Nair et al, Nature 2014, 516, 227. [2] M. Bartolomei, M. I. Hernández, J. Campos-Martínez, R. Hernández-Lamoneda, Carbon 2019, 144, 724. [3] S. M. Lee, K. H. An, G. Seifert, Y. H. Lee, T. Frauenheim, J. Am. Chem. Soc. 2001, 123, 5059. [4] Y. Feng, J. Chen, W. Fang, E.-G. Wang, A Michaelides, X.-Z. Li, J. Phys. Chem. Lett. 2017, 8,6009. [5] P. Merino, M. Svec, J. Martínez, P. Jelinek, P. Lacovig, M. Dalmiglio, S. Lizzit, P. Soukiassian, J. Cernicharo, J. Martín-Gago, Nat. Commun. 2014, 5, 3054., This work has the support of the Spanish grant FIS2017-84391-C2-2-P. Allocation of computing time by CESGA is acknowledged

4th SAMS, Madrid, Spain, 24 -27 September 2019, The interaction of atoms and molecules with carbonaceous layered materials is a topic of interest both from a fundamental and a more applied points of view. We have been recently working on the construction of reliable global potential energy surfaces for these systems and their application in different dynamical processes. There is an ample literature in which these processes are studied by Molecular Dynamics (MD) simulations and/or approximate quantum models. In this contribution we report three-dimensional wave packet calculations to study the interaction potential between graphene and graphite with rare gas atoms as well as the transport of {4,3}^He atoms through a periodic rigid mebrane of graphdiyne -a novel material composed of nanopores at regular distances- and also through a holey graphene model (with a force-field based on simple Lennard- Jones interactions). A good agreement is found between approximate quantum models and present calculation for the case of graphdiyne, with a much more pronounced differences for the transmission through nanoporous graphene.

IX Jornadas de Jóvenes Investigadores en Física Atómica y Molecular, Sevilla, 22 al 24 de marzo de 2017. -- https://j2ifam2017.wordpress.com/, Recent progress in the production of new two-dimensional (2D) nanoporous materials is attracting considerable interest for applications to isotope separation in gases. In this work we present an accurate quantum-mechanical model to study the transmission of an atom through a periodic 2D membrane. The time-dependent Schrödinger equation is solved by propagating a 3D wave packet and, from the calculation of the flux through a surface separating the incident and trasmitted waves, transmission probabilities and rate coefficients are obtained. This method is applied to the transmission of 3He and 4He through the subnanometer pores of graphdiyne, using an optimized force field from ab initio calculations [1]. Results on transmission rate coefficients and selectivity ratios will be presented and compared with estimations based in transition state theory (TST) [2]. Some new clues for the design of an optimal pore for isotope separation will be suggested and discussed., This work has been partially supported by the Spanish Ministerio de Economía y Competitividad grant FIS2013- 48275-C2-1-P. A.Gijón acknowledges the “Garantía Juvenil del CSIC” program for finantial support.

The Joint Iberian Meeting on Atomic and Molecular Physics (IBER), Barcelona, September 12-14th, 2017. -- http://iber2017.com/index.php

Santiago de Compostela, Facultade de Química,17-21 julio 2017. --http://www.bienalrsef2017.com/bienalrsef17/, Two-dimensional (2D) membranes composed by (sub-)nanometer pores are allowing gas separation applications at the molecular level[1]. Confinement provided by these pores can enhance quantum effects in the dynamics of light atoms and molecules, such as zero point energy (ZPE) and tunneling. As these effects are mass-dependent, they might be used for isotopic separation (quantum sieving). There is a large literature where these processes are studied by means of classical dynamics with quantum corrections or approximate quantum models. We believe that accurate quantum-mechanical calculations are crucial to assess the reliability of the more approximate methods. For instance, ZPE and tunneling work in opposite directions: while tunneling increases the transmission rate of a given species, ZPE causes the opposite effect since it involves a higher ¿effective¿ potential barrier. Thus, accurate calculations are needed to account for the delicate balance between the above mentioned quantum features and to search for another quantum effects that might play a role in the overall process. In this contribution we present simulations for the transmission of an atom through a rigid periodic 2D membrane using a recently reported three-dimensional wave packet (WP3D) propagation treatment[2]. Transmission probabilities and rate coefficients are presented for the transport of 3He and 4He through graphdiyne[3] as well as through a holey graphene model[4]. Results are compared with tunneling-corrected transition state theory (TST)[5] and the range of validity of this and other (reduced dimensionality) theories is discussed. The appearance of clear evidences of resonance features are also shown., The work is funded by Spanish MINECO grant FIS2013-48275-C2-1-P. A. G. thanks “Garantía Juvenil” C.S.I.C. program. Allocation of computing time by CESGA is also acknowledged.

ESPA 2016, Castellón de la Plana, Spain, June 28th to July 1st, 2016, The interaction of atoms and molecules with carbonaceous layered materials is a topic of interest both from a fundamental and a more applied points of view. Among the many possible applications, we have recently focused on the use of this compounds as filters at the molecular level1. To this end we have recently developed2 reliable global interaction potential energy surfaces (PES) that can properly describe the short as well as the long range region.The potentials are based on atom-bond (or tom-atom) additive pairwise sums where the parameters are derived from the polarizabatility of the interacting partners which are after that, fine-tuned exploiting ab-initio calculations at high level of theory of prototypical Rg-Coronene (or anulene) systems. The performance as molecular filters is studied with these PES and wave packet propagation3. We have found that quantum effects are important4 and that zero point energy of the motion along the surface is very important in the molecular sieving when using these porous 2D materials.

Conferencia invitada ; Mendoza, Argentina. 9th-13st of May 2016 ; http://photodynamics9.wixsite.com/phd9

ECLA 2016 ; CSIC, Madrid, Spain, 21-25 November 2016 ; http://www.ecla2016.com/index.php, Work supportes by the Spanish MINECO research grant FIS2013-48275-C2

Meeting: Algorithm Development and High-Performance Computing in Chemistry and Physics, Bratislava, Slovakia, March 21-22, 2016 ; http://web4.umb.sk/molim2016/, Recent progress in the fabrication of one-atom-thick membranes composed by sub- nanometer size pores is attracting considerable interest for applications to molecular and isotopic separation in gases. 1 In this contribution, we will present a new three-dimensional time-dependent wave-packet (TDWP) approach for the calculation of the probabilities of transmission of atoms through the pores of a two -dimensional membrane. The method is applied to the passage of 3He and 4He through graphdiyne, a recently synthesized carbon-based membrane exhibiting uniformly distributed triangular pores. 2 The interaction between the He atoms with the membrane is represented by a new force field based on accurate electronic structure calculations. 3 We are particularly interested in studying the interplay between tunneling and zero point energy effects in the 4He/3He selectivity (isotopic separation) as a function of the temperature. In this way, the results of the TDWP calculations will be discussed in comparison with a previous study based on tunneling-corrected transition state theory.4 In addition, we will briefly report on an on going study about the use of Feynman-Hibbs effective potentials for the calculation of the internal energies and structures of clusters of cononene molecules and several He or Ne atoms.

Cost Action Molim, Molecules in Motions, CM 1405; University Paris-Est Marne-La-Vallée, France, 27-29 August 2015, The interaction of He atoms with Polycyclic Aromatic Hydrocarbons (PAHS) or their extensions such as graphene, graphynes, and related carbon layered materials is a topic of interest in several areas that go from astrophysics to more fundamental research and technological applications. For the study of these interactions is necessary to compute reliable potential energy surfaces (PES's) that can properly describe the short as well as the long range region. We have recently reported a global PES for the interaction of He on the surface of the coronene, as well as that of graphene, that shows a good agreement with ab-initio estimations. In this talk we will present some new results concerning the energetic and structure of small Hen@Coronene clusters by means of Diffusion Monte Carlo (DMC) techniques. The dynamics of He atoms interacting with graphene and graphynes will be discussed based on our wave packet propagation code in full dimensions and within a reduced dimensionality model.

ISACC 2015, Madrid, 18-21 July, 2015; http://fama.iff.csic.es/con/ISACC2015/index-isacc-2.html, We will present recent results on the interaction and processes taken place between rare gases (mainly He) and carbon layered materials and their precursors or prototypes. In particular focus will be put in the characterization of the potential between the gas particle and the substrate, the way in which it can be fit to provide an adequate force field, as well as several results concerning the cluster formation, the evolution with size and the dynamics at the quantum level.

AFM 2015, Stony Brook University, Long Island, New York, USA, June 29th to July 3rd 2015; http://afm2015.functionalmaterials.org/

7 pags.; 7 figs.; 1 tab., Recent progress in the production of new two-dimensional (2D) nanoporous materials is attracting considerable interest for applications to isotope separation in gases. In this paper we report a computational study of the transmission of 4 He and 3 He through the (subnanometer) pores of graphdiyne, a recently synthesized 2D carbon material. The He−graphdiyne interaction is represented by a force field parametrized upon ab initio calculations, and the 4 He/3 He selectivity is analyzed by tunneling-corrected transition state theory. We have found that both zero point energy (of the in-pore degrees of freedom) and tunneling effects play an extraordinary role at low temperatures (≈20−30 K). However, both quantum features work in opposite directions in such a way that the selectivity ratio does not reach an acceptable value. Nevertheless, the efficiency of zero point energy is in general larger, so that 4 He tends to diffuse faster than 3 He through the graphdiyne membrane, with a maximum performance at 23 K. Moreover, it is found that the transmission rates are too small in the studied temperature range, precluding practical applications. It is concluded that the role of the in-pore degrees of freedom should be included in computations of the transmission probabilities of molecules through nanoporous materials. © 2015 American Chemical Society, The work has been funded by Spanish MINECO grant FIS2013-48275-C2-1-P. Allocation of computing time by CESGA (Spain) and support by the COST-CMTS Action CM1405 “Molecules in Motion (MOLIM)” are also acknowledged.

IBER 2015, 6-9th September 2015, Aveiro – Portugal; http://iber2015.web.ua.pt/, Graphynes are novel two-dimensional carbon-based materials that exhibit regular and uniformly distributed sub-nanometer pores (Fig. 1). These features make them very promising materials for gas filtration applications at the molecular level[1]. Our goal is to study the interaction and dynamics of transmission of small molecules through graphynes¿ pores from first principles quantum mechanics calculations. We will focus on the properties of graphdiyne (whose molecular precursor is shown in the center of FIG. 1) as a filter of 3He from 4He. Accurate electronic structure calculations have served to obtain a new force field suitable for molecular dynamics simulations[2]. By means of the Transition State Theory (TST)[3] we have analyzed the role of tunneling as well as of the in-pore degrees of freedom in the selectivity for isotopic separation[4]. In addition, we will present preliminary three-dimensional time-dependent wave-packet calculations of the transmission of the 3He and 4He through the graphynes¿ pores, which will allow us to compare with the results from the TST as well as with previous one-dimensional wave-packet simulations[2]. [1] S. W. Cranford and M. J. Buehler, Nanoscale 4, 4587 (2012) [2] M. Bartolomei, E. Carmona-Novillo, M. I. Hernández, J. Campos-Martínez, F. Pirani, G. Giorgi, J. Phys. Chem. C 118, 29966 (2014) [3] M. Hankel et al., Phys Chem. Chem. Phys. 13, 7834 (2011) [4] M. I. Hernández, M. Bartolomei, J. Campos-Martínez, in preparation.

Conferencia invitada; Oaxaca, México, 27th-31st of October 2014. http://www.photodynamics.hol.es/index.php, A detailed knowledge of the collisional excitation of water by He is very important for the modeling of water-rich regions in the interstellar medium. Since the pioneering calculations of the H2O-He potential energy surface (PES) and rotationally inelastic rate coefficients by Green et al [1], several improved calculations of PESs have been reported more recently [2-4]. Rate coefficients may be substantially different using one or another PES due to the high sensitivity of the dynamics to their features. We will report a combined experimental-theoretical study for the determination of the state-to-state rate coefficients of ortho- and para-H2O:He inelastic collisions in the 20-120 K thermal range. In the experiment, the H2O rotational populations along a supersonic jet of a mixture of He and highly diluted H2O are accurately measured using Raman spectroscopy. On the other hand, rate coefficients are computed by means of closecoupling calculations using the different PESs [2-4]. These calculations are tested against the experiments through a detailed analysis of the kinetic Master equation which combines both experimental and theoretical data. It is found that the rates based on the Hodges[2] and Patkowski[3] PESs agree with experiment within 15%, while the rates by Green[1] are between 25-40% too low. In this contribution, we will give an analysis of the different H2O-He PESs and their effects on the rotationally inelastic dynamics. This assessment will be completed by calculations of total integral cross sections in comparison with molecular beam experiments[5]. Finally, a preliminary estimation of water-water rate coefficients (affecting less diluted mixtures) will be reported.

Bologna, Italy, September 2-6, 2014 ; http://www.chem.uni-wuppertal.de/conference/, High-resolution Raman spectroscopy has been employed to study the O2:He inelastic collisions at temperatures from 10 to 40 K. For that purpose, a number of supersonic microjets of O2:He mixtures free from O2 condensation, with O2 mole fractions ranging from 0.025 to 0.50, have been quantitatively characterized in terms of number densities n(z) and rotational populations PJ(z) along the jet direction (z) by means of the rotational and vibrational Raman spectra. Number densities n(z) were obtained by comparing the intensity of the fundamental Q-branch at 1555 cm-1 in the jet with that from a static sample at a known number density, while rotational populations are extracted from the integrated intensities of the triplets associated with the N->N+2 Raman transitions, N being the rotational angular momentum [1]. These primary data are reduced to rotational TROT(z) and translational TTRA(z) temperatures. Translational temperatures have been obtained from number densities and rotational temperatures by conservation of mass, momentum, and enthalpy along the jet [2]. These measurements can be linked to calculations of state-to-state rate coefficients by means of the kinetic Master Equation, which accounts for the time evolution of the rotational populations. The rate coefficients have been computed [3] by solving the close-coupling equations for O2 + He collisions and using an accurate ab initio potential energy surface [4]. A careful analysis of the Master Equation, which combines experimental and theoretical data, allows us to assess the accuracy of the rate coefficients and, in turn, of the potential energy surface.

Workshop “Helium-mediated Synthesis, Soft-landing and Spectroscopy of Metal Nanoparticles on Surfaces”, CSIC, Madrid, Spain, October 10-11, 2014, The interaction between rare-gas atoms with graphene type surfaces is a topic of great interest given the many applications of these materials that can be foreseen. For example, some porous derivatives, have been proposed as a nano-scale membrane which could be used as an atmospheric nanofilter[1]. For most of these studies it is necessary not only a reliable and accurate description of the interaction potential but it is also fundamental to obtain a convenient parametrization to support dynamical studies on the physisorption of atoms or molecules. We report reliable global potentials for the physisorption of rare gases with graphene and graphite surfaces amenable for a variety of dynamics simulations[2]. An atom-bond pairwise additive form of the potential is used, where the interaction pairs are constituted by the Rg atom (Rg= He, Ne, Ar, Kr) and the C-C bonds of the graphene sheet(s). The parameters of the atom-bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned exploiting calculations of the prototypical Rg-coronene system through high level electronic structure methods. The atom- graphene/graphite potential is further expanded in a Fourier series that only requires a small number of corrugation terms. Our results results are found to compare well with previous data[3] regarding well depths and equilibrium distances at different adsorption sites. Diffraction intensities are more sensitive and results based on Close-Coupled calculations[4] are shown for the system He-graphene.

International Conference on Structural Nano Composites, Consejo Superior de Investigaciones Científicas (CSIC), 20-21 May (2014)

5th International Meeting on Atomic and Molecular Physics and Chemistry, Salamanca (Spain) 8 – 11 July (2014); http://imampc2014.usal.es/

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 ab initio global potential energy surface (PES) for the O2(3∑g -) + N 2(1∑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 of the interaction potential containing a large number of terms due to the anisotropy of the interaction has been built from the ab initio data. The expansion coefficients, which are functions of the intermolecular distance, are matched in the long-range with the analytical functions based on the recent ab initio calculations of the electric properties of the monomers [ M. Bartolomei et al. J. Comput. Chem. 2011, 32, 279 ]. 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 lowest lying 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. © 2014 American Chemical Society., We thank financial support by Spanish grant FIS2010-22064-C02-02.

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

The work has been funded by the Spanish Grant FIS2010-22064-C02-02. We also thank the COST-CMTS Action CM1002 “CODECS” for support and CESGA for allocation of computing time.

CODECS 2013 Workshop. Convergent Distributed Environment for Computational Spectroscopy, San Lorenzo de El Escorial, Madrid, 18th – 22nd April, 2013 http://fama.iff.csic.es/con/COST2013/codecs2013-boa.pdf, The interaction between atoms and molecules with graphene type surfaces is a topic of great interest given the potential new applications of these materials. For example it is in principle possible to detect with high resolution the presence of a single atom adsorbed on these surfaces1; also its porous sheets synthesized with atomic precision2 have been proposed as a nano-scale membrane which could be used as an atmospheric nanofilter3. Thus in this kind of studies it is necessary not only a reliable and accurate description of the interaction potential but it is also fundamental to obtain a convenient parametrization of the involved non-covalent interactions to support dynamical studies on the physisorption of atoms and molecules. We report reliable global potentials for the physisorption of rare gases with graphene and graphite surfaces amenable for a variety of dynamics simulations. An atom-bond pairwise additive form4 of the potential is used, where the interaction pairs, represented by proper analytical functions, are constituted by the Rg atom (Rg= He, Ne, Ar, Kr) and the C-C bonds of the graphene sheet(s). The parameters of the atom-bond pair potential, derived from the polarizability of the interacting partners, are fine-tuned exploiting calculations of the prototypical Rg--coronene system(see Fig. 1) using high level electronic structure methods, such as DFT-SAPT5 and MP2C6, and large basis sets. The atom-graphene/graphite potential is further expanded in a Fourier series and it is found that, for an accurate representation of the interaction, only a small number of corrugation terms need to be added to the laterally averaged potential. Furthermore, this corrugation part of the potential is identical for both Rg--graphene and Rg--graphite; in other words, inner layers of graphite only play a role in the laterally averaged Rg-graphite potential. For all systems, the hollow at the center of the carbon ring is preferred over the bridge and top adsorption sites (see Fig. 1), although diffusion barriers are low. Present results7 are found to compare well with previous data8 regarding well depths and equilibrium distances at different adsorption sites and, for graphite, the long-range dispersion coefficient C3. Moreover for Rg-graphene an estimation of the long-range dispersion coefficient C4 is provided for the first time. In addition, the interaction between Rg and porous graphene is modeled and barriers for penetration through the pores have been obtained; a potential use for ligther gases separation from the heavier ones is proposed.

IBER 2013, XII Iberian Meeting on Atomic and Molecular Physics, Univ. Pablo de Olavide, Sevilla, Sept. 9-11 (2013), The interaction between molecules and graphene is a topic of great interest. For instance, porous graphene films that could be used as nanofilters of atmospheric molecules have been recently synthesized[1]. To carry out computational simulations of this type of processes, it is desirable to employ realistic interaction potentials given by simple functional forms. We report global interaction potentials for the physisorption of rare gas (Rg= He, Ne, Ar and Kr) atoms on graphene and graphite[2]. An atom-bond pair-wise additive representation is used, where the interaction pairs are constituted by the Rg atom and the C-C bonds of the graphene sheet(s). The parameters of the analytical function describing the atom-bond potential are derived from the polarizabilities of the interaction partners and, in a second step, they are fine-tuned from accurate ab initio calculations of the prototypical Rg-coronene system. The Rg-graphene/graphite interaction potential obtained in this way is further expanded in a Fourier series and the corresponding coefficients are fitted to simple functional forms. Well depths and equilibrium distances compare quite well with several recent calculations. Moreover, the long range dispersion coefficient C3 and the calculated binding energies of Rg-graphite are in a rather good agreement with experimental determinations. The calculations are being extended to small molecules (H2, CH4), as well as to the study of the interaction of Rg atoms with porous graphene.

International Workshop on Architecture & Design of Molecule Logic Gates and Atom Circuits, Barcelona, from 12th to 13th of January 2012 Read more: International Workshop on architecture and design of molecule logic gates and atom circuits

International Meeting on Atomic and Molecular Physics and Chemistry, Scuola Normale Superiore Pisa, Italy 12-14 September 2012

APS March Meeting 2012 Volume 57, Number 1 Monday–Friday, February 27–March 2 Boston, Massachusetts (2012)

International workshop on Coherence and Decoherence at Ultracold Temperatures, Munich, September 6-9 2011. http://www.ultracoldca.pwias.ubc.ca/

Quantum information processing and communication international conference, ETH Zurich, September 5-9, 2011. http://www.qipc2011.ethz.ch/

International Meeting on Atomic and Molecular Physics and Chemistry, Rennes, (France), 5-8 July 2011.

XVIII European Conference on Dynamics of Molecular, University of Coimbra at Curia-Anadia, Portugal, September 5-10, 2010. http://www.molec2010.uc.pt/

I International Meeting on Atomic and Molecualr Physics and Chemistry, Madrid, June 29-July 2, 2010

QSCP XV - Fifteenth International Workshop on Quantum Systems in Chemistry on Physics, Magdalene College, University of Cambridge, 31dt August-5th September 2010

I International Meeting on Atomic and Molecualr Physics and Chemistry, Madrid, June 29-July 2 2010

I International Meeting on Atomic and Molecualr Physics and Chemistry, Madrid, June 29-July 2, 2010. http://fama.iff.csic.es/con/imampc-2010/, The energy transfer by collisions involving the ground and excited species of molecular oxygen plays a crucial role in the chemistry of the upper Earth¿s atmosphere. The specificities of molecular oxygen (a stable radical in its ground X 3¿g - state, with two low-lying excited states a 1¿g and b 1¿g +) provide appropriate conditions for a rich variety of collision-induced energy transfer mechanisms. Experimentally, the rate coefficients measured for the collisional removal of O2(X 3¿g -, high-v),O2(a 1¿g, low-v) and O2(b 1¿g +, low-v) by O2 are fast and show peculiar features which cannot be explained by simple vibrational cascadings. The strong changes observed in the rate coefficients between adjacent vibrational levels suggest that near-resonant processes, involving electronic energy transfers, should dominate the removal processes. However, the final state distribution could not be probed experimentally, and theoretical studies are needed to unveil the underlying mechanisms. By resorting to a reduced dimensionality model of the dimer, together with ab initio methods and quantum dynamics calculations, we have shown that intra-molecular electronic energy transfers, O2(X 3¿g -, v) + O2 ¿ O2(a 1¿g, v¿) + O2, O2(X 3¿g -, v) + O2 ¿ O2(b 1¿g +, v¿) + O2, mediated by spin-orbit couplings between the dimer states, were able to mimic the sharp changes observed in the measured collisional removal rate coefficients for O2(X 3¿g -,v ¿ 26). In a recent study, we have also addressed the problem of inter-molecular electronic energy transfer, O2(b 1¿g+, v) + O2(X 3¿g-, v=0) ¿ O2(X 3¿g -, v¿) + O2(b 1¿g+, v=0), mediated by nonadiabatic radial couplings between the dimer states. It is found that the multidimensional nonadiabatic couplings can be predicted with high accuracy, compared to the ab initio results, by using analytical forms only depending on a reduced set of adiabatic energy terms. The results of quantum dynamics calculations for the removal of O2(b 1¿g +, v ¿ 3) are found qualitatively consistent with the experimental observations.