Descripción: We analyze the doubly-differential momentum distributions of electrons ejected at the interaction of strong IR laser pulses with atoms. With the help of a semiclassical model we clarify the interplay between intracycle and intercycle interferences. The model results are compared with numerical solutions of the time-dependent Schrödinger equation for atoms with long-range potentials. Similarities and differences will be discussed. © Published under licence by IOP Publishing Ltd.

Descripción: We study the dependence of the magnetic properties of NiPd and CoPd segregated nanoclusters and slabs as a function of the 3d magnetic component concentration (x), the chemical order, and size. In the case of clusters we consider 3d cores coated by Pd atoms (3d/Pd) and also onion-like (Pd/3d/Pd) configurations. For the slabs we consider different possible segregated structures of the 3d and 4d atoms and study the evolution of the magnetic properties on these different configurations. We show that Pd coating gives rise to an enhancement of the average magnetic moment of the Ni or Co core atoms and of the Pd atoms as well. Larger values of the average magnetic moments are obtained in the onion-like structures (Pd/3d/Pd) than in the core/shell (3d/Pd) configuration. We compare with theoretical and experimental results available in the literature.

Descripción: In this work we investigate experimentally and theoretically angular distributions of swift multi-electronic atoms after colliding with a LiF(001) surface under axial surface channeling conditions. We use the surface eikonal approximation to describe the quantum interference of scattered projectiles. The atom-surface interaction is represented by means of a pairwise additive potential that includes the contribution of the projectile polarization. The aim is to use the experimental spectra to test the range of validity of the proposed potential model. © Published under licence by IOP Publishing Ltd.

Descripción: Multiple ionization cross sections of Ne atoms are reported for Li 3+ impact in the energy range of 2 to 5.8MeV. The neon ionization cross sections were separated into three collision channels, namely; direct ionization (DI), single capture (SC) and transfer ionization (TI). The direct ionization data is compared to CDW-EIS calculations as well as to other projectiles with charge state q 3+. The single capture is compared to a modified Bohr-Lindhard semi classical model.

Descripción: This work describes simple decompositions of the energy of molecular systems according to schemes that partition the three-dimensional space. The components of those decompositions depend on one and two atomic domains thus providing a meaningful chemical information about the nature of different bondings among the atoms which compose the system. Our algorithms can be applied at any level of theory (correlated or uncorrelated wave functions). The results reported here, obtained at the Hartree-Fock level in selected molecules, show a good agreement with the chemical picture of molecules and require a low computational cost in comparison with other previously reported decompositions.

Descripción: This work describes a simple spatial decomposition of the first-order reduced density matrix corresponding to an N -electron system into first-order density matrices, each of them associated to an atomic domain defined in the theory of atoms in molecules. A study of the representability of the density matrices arisen from this decomposition is reported and analyzed. An appropriate treatment of the eigenvectors of the matrices defined over atomic domains or over unions of these domains allows one to describe satisfactorily molecular properties and chemical bondings within a determined molecule and among its fragments. Numerical determinations, performed in selected molecules, confirm the reliability of our proposal. © 2005 American Institute of Physics.

Descripción: A projectile ion-recoil ion and electron-recoil ion coincidence technique has been used to study the multiple ionization process in collisions of 0.75-4.0MeV B2+ with Ne atoms. Absolute total and partial pure ionization cross sections are reported for the first time at these impact energies with the present setup. The relative contribution of each recoil charge state has been investigated. The experimental data are compared to CDW-EIS calculation and with He2+ projectiles. The data throw further light on the effect of projectile screening in the ionization of multi-electronic targets and provide a support for the validity of the CDW-EIS model in this intermediate-to low velocity regime.

Descripción: A simple model that employs a periodic, planar array of parallel cylinders representing the nanotubes is presented. Using this method, the existence of several phase transitions in the film is demonstrated. These include both two-dimensional (2D) transitions and quasi-1D transitions.

Descripción: The post-collisional interactions in ion-atom ionization collisions are studied around the electron capture to the continuum (ECC) process. For this purpose, a suitable double differential cross section is introduced, involving the longitudinal recoil-ion momentum and the projectile transverse momentum transfer. Using the fact that the ECC process is closely related to the threshold in the longitudinal momentum distribution, we study this distribution as a function of the projectile scattering angle. Using the CDW-EIS approximation we theoretically find a focusing (defocusing) effect as we get closer to the distribution threshold for proton (antiproton) impact on He atoms. © 2007 IOP Publishing Ltd.

Descripción: In this paper we generalize an interpolation result due to J.-O. Strömberg and A. Torchinsky to the case of one-sided Hardy spaces. This generalization is important in the study of the weak type (1,1) for lateral strongly singular operators. We shall need an atomic decomposition in which for every atom there exists another atom supported contiguously at its right. In order to obtain this decomposition we have developed a rather simple technique to break up an atom into a sum of others atoms. © 2006 by Institut Mittag-Leffler. All rights reserved.

Descripción: The crystal structure of the title complex, [Ni(C3H4N2)6](C4H 4O5)·C2H5OH, is a tightly woven three-dimensional network composed of [Ni(Him)6]2+ cations (Him is imidazole) interlinked by the oxydiacetate anion through six different N-H⋯O bonds, in which all the N-H imidazole groups, as well as all the carboxylate O atoms, take part. This structure is the first to show an [Ni(Him)6]2+ group which does not display any crystallographic symmetry. © 1999 International Union of Crystallography.

Descripción: The title complex, aqua(2,2′-bipyridy-N,N′(3-thiapentanedioate-O,S,O′)zinc(II) tetrahydrate, [Zn(C4H4-O4S)(C10H8N 2)(H2O)].4H2O, is mononuclear with a coordination sphere consisting of one S, two N and three O atoms. The Zn atom is linked to a tridentate thiodiacetate ligand, a bidentate 2,2′-bipyridine ligand and an aqua ligand resulting in a slightly distorted octahedral coordination geometry. The molecular units are linked together in the crystal by an extensive hydrogen-bonding network and by intermolecular S⋯S interactions.

Descripción: This paper describes a matrix formulation for the correlated hole theory within the framework of the domain-averaged model in many electron systems (atoms, molecules, condensed matter, etc.). General relationships between this quantity and one-particle reduced density matrices for any independent particle or correlated state functions are presented. This formulation turns out to be suitable for computational purposes due to the straightforward introduction of cumulants of two-particle reduced density matrices within the quantum field structure. Numerical calculations in selected simple molecular systems have been performed in order to determine preliminary correlated values for such a quantity.

Descripción: The resolution of molecular electric dipole polarizabilities into atomic contributions was studied in the context of methyl and ethyl derivatives, CH3-X and CH3-CH2-X. The reliability of the partitioning schemes allowing for adhoc quantum chemical tools was also tested. Results depicted a good degree of the transferability from molecule to molecule as shown by the evaluation of gross atomic isotropic contributions for carbon, hydrogen, and heteroatoms.

Descripción: The structures of three new polymeric lanthanide complexes, poly[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato- digadolinium(III)] tetra-hydrate], {[Gd 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇4H 2O} n , (I),poly[diaqua-(2,2′- bipyridine)di-μ3-itaconato-μ2-ita-conato-digadolinium(III)], [Gd 2(C 5H 404) 3(C 10H 8N 2)(H 2O) 2] n , (II), and poly-[[bis-(2,2′-bipyridine)-μ4-itaconato-di-μ3-itaconato-di- holmium(III)] dihydrate], {[Ho 2(C 5H 4O 4) 3(C 10H 8N 2) 2]̇2H2O} n , (III), have been solved from twinned specimens. Compound (I) presents a two-dimensional polymeric structure parallel to (011) built up around two independent nine-coordinated Gd centres displaying similar GdO 7N 2 environments, with both N-donor atoms in each provided by a chelating 2,2′-bipyridine (bpy) unit. The coord-inating O atoms are from three different itaconate (ita) anions (itaconic acid is 2-methyl-idene-butane-dioic acid). Compound (II) also presents two independent Gd centres (one ten- and the other ight-coordinated), but the overall formula and individual coordinations are different from those of (I). The chemical unit is in this case completed by one bpy ligand, three ita anions (one of them displaying a new, hitherto unreported, mu;3-O,O′:O′,O′′: O′′′ binding mode) and two aqua ligands. The whole structure is built up around a twofold rotation axis passing through both cations, as well as through the centre of the bpy ligand and one of the ita anions, thus making only half of the chemical unit independent. Finally, compound (III) presents a single independent Ho centre, a bpy unit and one and a half ita anions (one of them bisected by a twofold rotation axis) in the asymmetric unit, plus two (disordered) nonbonded solvent water mol-ecules. In compounds (II) and (III), those ita anions bisected by a symmetry element incompatible with the inter-nal symmetry of the ligand exhibit disorder in the C=CH 2 group. © 2009 International Union of Crystallography.

Descripción: We theoretically analyze the multiple-scattering effects that might occur in the ionization of a molecule by the impact of photons or massive particles, by calculating the series to all orders within a muffin-tin description. We find a large sensitivity on the final state and a sizable momentum-dependent distortion of the phase-shift and frequency of the interference oscillations, that are not replicated by non-scattering or single-scattering approximations. Furthermore, our results do not validate the existence of any discernible harmonic oscillations. © Published under licence by IOP Publishing Ltd.

Descripción: In contrast to the wide spectrum of cytochrome P450 monooxygenases, there are only 2 heme-based dioxygenases in humans: tryptophan dioxygenase (hTDO) and indoleamine 2,3-dioxygenase (hIDO). hTDO and hIDO catalyze the same oxidative ring cleavage reaction of L-tryptophan to N-formyl kynurenine, the initial and rate-limiting step of the kynurenine pathway. Despite immense interest, the mechanism by which the 2 enzymes execute the dioxygenase reaction remains elusive. Here, we report experimental evidence for a key ferryl intermediate of hIDO that supports a mechanism in which the 2 atoms of dioxygen are inserted into the substrate via a consecutive 2-step reaction. This finding introduces a paradigm shift in our understanding of the heme-based dioxygenase chemistry, which was previously believed to proceed via simultaneous incorporation of both atoms of dioxygen into the substrate. The ferryl intermediate is not observable during the hTDO reaction, highlighting the structural differences between the 2 dioxygenases, as well as the importance of stereoelectronic factors in modulating the reactions.

Descripción: An alternative approach for the calculation of the electron-positron (e-p) contribution to magnetic properties based on two-component Breit-Pauli spinors is presented. In it, the elimination of the small component scheme is applied to the inverse propagator matrix of e-p pairs. The effect of the positronic manifold is expressed as an operator acting on Breit-Pauli spinors. The operator form thus obtained sums up the relativistic correction as a geometric series and as a result a totally different behavior in the vicinity of a nucleus is obtained as compared to the one of the linear response approximation. This feature has deep influence in numerical values of the e-p contribution to the nuclear magnetic shielding of heavy atoms. Numerical calculations carried out for Kr, Xe, and I show that with this approach, the e-p contributions to this property are in good agreement with those of four-component methods. © 2009 American Institute of Physics.

Descripción: The molecular structure of the title compound, [Zn(CH3COO) 2(C12H12N2)], consists of isolated molecules bisected by a twofold rotation axis which goes through the ZnII cation and halves the organic base through the central C-C bond. The Zn II ion is coordinated by two N atoms from one molecule of the aromatic base and four O atoms from two bidentate, symmetry-related acetate anions, which coordinate asymmetrically [Zn-O distances of 2.058(2) and 2.362(3)Å], while the two Zn-N bond distances are equal as imposed by symmetry [2.079(2)Å]. The crystal structure is supported by a number of weak C-H⋯O interactions and C-H⋯π contacts, with no π-π interactions present, mainly hindered by the substituent methyl groups and the relative molecular orientation. The result is a three-dimensional structure in which each molecule is linked to eight different neighbors.