Estela Carmona-Novillo

The N2–N2 system: An experimental potential energy surface and calculated rotovibrational levels of the molecular nitrogen dimer

An accurate new representation for the potential energy surface for the N2–N2 dimer has been obtained from the analysis of scattering experiments from our laboratory, and of available second virial coefficient data. A harmonic expansion functional form describes the salient geometries of the dimer and accounts for the relative contributions to the intermolecular interaction from components of different nature. The equilibrium geometry is a T conformation with well depth 13.3 meV (107.14 cm−1) and at a distance of 4.03 A. In order to assist in the analysis of spectra, we calculated the bound rotovibrational states for the (N2)2 system for J⩽6 by solving a secular problem over the exact Hamiltonian, considering the N2 monomers as rigid rotors, and where the Coriolis coupling is included.

Penetration Barrier of Water through Graphynes’ Pores: First-Principles Predictions and Force Field Optimization

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.

Graphdiyne Pores: “Ad Hoc” Openings for Helium Separation Applications

Graphdiyne is a novel two-dimensional material deriving fr om graphene that has been recently synthesized and featuring uniformly distributed su b-nanometer pores. We report accurate calculations showing that graphdiyne pores permit an a lmost unimpeded helium transport which can be used for its chemical and isotopic separation. E xceptionally high He/CH4 selectivities are found which largely exceed the performance of t he best membranes used to date for extraction from natural gas. Moreover, by exploiting sl ight differences in the tunneling probabilities of3He and4He, we also find promising results for the separation of the fe rmionic isotope at low temperature. To whom correspondence should be addressed †Instituto de Física Fundamental, Consejo Superior de Inves tigaciones Científicas (IFF-CSIC), Serrano 123, 28006 Madrid, Spain ‡Dipartimento di Chimica, Biologia e Biotecnologie, Univer sità di Perugia, Perugia, Italia ¶Department of Chemical System Engineering, School of Engin eeri g, University of Tokyo, Tokyo, Japan

The asymmetric dimer N2–O2: Characterization of the potential energy surface and quantum mechanical calculation of rotovibrational levels

The potential energy surface for the N2–O2 system has been characterized through a combined analysis of scattering experiments and second virial coefficient data. A spherical harmonic expansion functional form has been used to describe the intermolecular features in the salient geometries of the complex and to account for the relative contributions arising from interaction components of different nature. The most stable geometry is an X conformation where the potential well exhibit a depth of −16.08 meV at a distance of 3.66 A. In order to relate structure dynamics and spectroscopic features of this weakly bound asymmetric dimer, we carried out extensive calculations of the bound rotovibrational states permitted to the complex. Calculations have been carried out with both exact and approximate quantum mechanical methods, where, respectively, the Coriolis coupling is both included and neglected.

Dimers of the major components of the atmosphere: Realistic potential energy surfaces and quantum mechanical prediction of spectral features

Accurate potential energy surfaces for the N2–N2 and N2–O2 dimers have been obtained from the analysis of scattering experiments from our laboratory, and of available second vi rial coefficient data. A harmonic expansion functional form describes the geometries of the dimers and accounts for the relative contributions to the intermolecular interaction from components of different nature. Together with the previously obtained singlet, triplet and quintet O2–O2 surfaces, where the role of spin–spin coupling was also considered, the new surfaces allow the full characterization of structure and internal dynamics of the clusters, whose bound states and eigenfunctions are obtained by exact quantum mechanics. Besides the information on the nature of the bond, these results can be of use in modelling the role of dimers in air. The calculated rotovibrational levels also provide a guidance for the analysis of spectra, thus establishing the ground for atmospheric monitorings.

Global ab initio potential energy surfaces for the O2(Σ3g−)+O2(Σ3g−) interaction

Completely ab initio global potential energy surfaces (PESs) for the singlet and triplet spin multiplicities of rigid O(2)((3)Σ(g)(-))+O(2)((3)Σ(g)(-)) are reported for the first time. They have been obtained by combining an accurate restricted coupled cluster theory with singles, doubles, and perturbative triple excitations [RCCSD(T)] quintet potential [Bartolomei et al., J. Chem. Phys. 128, 214304 (2008)] with complete active space second order perturbation theory (CASPT2) or, alternatively, multireference configuration interaction (MRCI) calculations of the singlet-quintet and triplet-quintet splittings. Spherical harmonic expansions, containing a large number of terms due to the high anisotropy of the interaction, have been built from the ab initio data. The radial coefficients of these expansions are matched at long range distances with analytical functions based on recent ab initio calculations of the electric properties of the monomers [M. Bartolomei, E. Carmona-Novillo, M. I. Hernández, J. Campos-Martínez, and R. Hernández-Lamoneda, J. Comput. Chem. (2010) (in press)]. The singlet and triplet PESs obtained from either RCCSD(T)-CASPT2 or RCCSD(T)-MRCI calculations are quite similar, although quantitative differences appear in specific terms of the expansion. CASPT2 calculations are the ones giving rise to larger splittings and more attractive interactions, particularly in the region of the absolute minima (in the rectangular D(2h) geometry). The new singlet, triplet, and quintet PESs are tested against second virial coefficient B(T) data and, their spherically averaged components, against integral cross sections measured with rotationally hot effusive beams. Both types of multiconfigurational approaches provide quite similar results, which, in turn, are in good agreement with the measurements. It is found that discrepancies with the experiments could be removed if the PESs were slightly more attractive. In this regard, the most attractive RCCSD(T)-CASPT2 PESs perform slightly better than the RCCSD(T)-MRCI counterpart.

Accurate ab initio intermolecular potential energy surface for the quintet state of the O2(Σg−3)–O2(Σg−3) dimer

A new potential energy surface (PES) for the quintet state of rigid O(2)((3)Sigma(g)(-)) + O(2)((3)Sigma(g)(-)) has been obtained using restricted coupled-cluster theory with singles, doubles, and perturbative triple excitations [RCCSD(T)]. A large number of relative orientations of the monomers (65) and intermolecular distances (17) have been considered. A spherical harmonic expansion of the interaction potential has been built from the ab initio data. It involves 29 terms, as a consequence of the large anisotropy of the interaction. The spherically averaged term agrees quite well with the one obtained from analysis of total integral cross sections. The absolute minimum of the PES corresponds to the crossed (D(2d)) structure (X shape) with an intermolecular distance of 6.224 bohrs and a well depth of 16.27 meV. Interestingly, the PES presents another (local) minimum close in energy (15.66 meV) at 6.50 bohrs and within a planar skewed geometry (S shape). We find that the origin of this second structure is due to the orientational dependence of the spin-exchange interactions which break the spin degeneracy and leads to three distinct intermolecular PESs with singlet, triplet, and quintet multiplicities. The lowest vibrational bound states of the O(2)-O(2) dimer have been obtained and it is found that they reflect the above mentioned topological features of the PES: The first allowed bound state for the (16)O isotope has an X structure but the next state is just 0.12 meV higher in energy and exhibits an S shape.

Molecular oxygen tetramer (O2)4: intermolecular interactions and implications for the epsilon solid phase

Recent data have determined that the structure of the high pressurephase of solid oxygen consists of clusters composed of four O2 molecules. This finding has opened the question about the nature of the intermolecular interactions within the molecular oxygen tetramer. We use multi- configurational ab initio calculations to obtain an adequate characterization of the ground singlet state of (O2)4 which is compatible with the non magnetic character of thephase. In contrast to previous suggestions implying chemical bonding, we show that (O2)4 is a van der Waals like cluster where exchange interactions preferentially stabilize the singlet state. However, as the clus- ter 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 �-oxygen.

Quantum mechanics of molecular oxygen clusters: rotovibrational dimer dynamics from realistic potential energy surfacesPresented at the Second International Conference on Photodynamics, Havana, Cuba, February 10???16, 2002.Electronic supplementary information (ESI) available: energy of the dimer in the first rovibrational levels or in the lowest rotovibrational states of A1 symmetry at J ??? 6 (Tables S1???S4). See http://www.rsc.org/suppdata/cp/b2/b203772f/

The three low-lying potential energy surfaces in the O2–O2 dimer, describing the dependence of the interaction on the intermolecular distance and on the relative molecular orientation, had been accurately characterized from the analysis of scattering experiments carried out by using polarized O2 beams, generated and selected under angular and velocity resolution conditions suitable to measure quantum interference effects in the velocity dependence of the integral cross sections. Most of the bonding in the dimer was found to come from van der Waals forces, but in this open shell-open shell system chemical (spin–spin) contributions, to the ground state interaction at the equilibrium, are ∼15%. This complete characterization of the potential energy surfaces, of interest also for the theory of weak chemical bond and crucial to define structure, dynamics and spectroscopic features of the complex, is exploited in this paper to calculate the bound rotovibrational states for the O2–O2 dimer for J ⩽ 6 by solving a secular problem over the exact Hamiltonian, considering O2 monomers as rigid rotors, and where the Coriolis coupling is included, allowing the assessment of the limits of the centrifugal sudden approximations. The results of this study are of relevance for the analysis of spectra and the description of characteristic internal motions for this prototypical weakly bound molecular complex.

Global ab initio potential energy surface for the O2((3)Σ(g)(-)) + N2((1)Σ(g)(-)) 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 ab initio global potential energy surface (PES) for the O2((3)Σg(–)) + N2((1)Σg(+)) 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.