Steps on Pt stereodynamically filter sticking of O2

Low coordinated sites on catalytic surfaces often enhance reactivity, but the underlying dynamical processes are poorly understood. Using two independent approaches, we investigate the reactivity of O2impinging onto platinum and resolve how step edges on (111) terraces enhance sticking. At low incident energy, the linear dependence on step density, independence of step type, and insensitivity to O2’s molecular alignment show that trapping into a physisorbed state precedes molecular chemisorption and dissociation. At higher impact energies, direct molecular chemisorption occurs in parallel on steps and terraces. While terraces are insensitive to alignment of the molecule within the (111) plane, steps favor molecules impacting with their internuclear axis parallel to the edge. Stereodynamical filtering thus controls sticking and dissociation of O2on Pt with a twofold role of steps.

Crystal structure ofcatena-poly[hemi[1,3-bis(2,6-diisopropylphenyl)imidazolium] [[μ3-acetato-κ3O:O:O′-tri-μ2-acetato-κ6O:O′-dicopper(II)(Cu—Cu)]-μ-chlorido] dichloromethane sesquisolvate]

The title copper(II) complex, {(C27H37N2)[Cu4(CH3COO)8Cl]·3CH2Cl2}n, is a one-dimensional coordination polymer. The asymmetric unit is composed of a copper(II) tetraacetate paddle-wheel complex, a Cl−anion situated on a twofold rotation axis, half a 1,3-bis(2,6-diisopropylphenyl)imidazolium cation (the whole molecule being generated by twofold rotation symmetry) and one and a half of a dichloromethane solvent molecule (one being located about a twofold rotation axis). The central metal-organic framework comprises of a tetranuclear copper(II) acetate `paddle-wheel' complex which arises from the dimerization of the copper(II) tetraacetate core comprising of three μ2-bidentate acetate and one μ3-tridentate acetate ligands per binuclear paddle-wheel complex. Both CuIIatoms of the binuclear component adopt a distorted square-pyramidal coordination geometry (τ = 0.04), with a Cu...Cu separation of 2.6016 (2) Å. The apical coordination site of one CuIIatom is occupied by an O atom of a neighbouring acetate bridge [Cu—O = 2.200 (2) Å], while that of the second CuIIatom is occupied by a bridging chloride ligand [Cu...Cl = 2.4364 (4) Å]. The chloride bridge is slightly bent with respect to the Cu...Cu internuclear axis [Cu—Cl—Cu = 167.06 (6)°] and the tetranuclear units are located about a twofold rotation axis, forming the one-dimensional polymer that propagates along [101]. Charge neutrality is maintained by the inclusion of the 1,3-bis(2,6-diisopropylphenyl)imidazolium cation within the crystal lattice. In the crystal, the cation and dichloromethane solvent molecules are linked to the coordination polymer by various C—H...O and C—H...Cl hydrogen bonds. There are no other significant intermolecular interactions present.

Electric field induced crossings of energy terms of a Rydberg quasi molecule enhancing charge exchange and ionization

Charge exchange is one of the most important atomic processes in plasmas. Charge exchange and crossings of corresponding energy levels that enhance charge exchange are strongly connected with problems of energy losses and of diagnostics in high temperature plasmas. Charge exchange was also proposed as an effective mechanism for population inversion in the soft X-ray and vacuum ultraviolet ranges. One of the most fundamental theoretical domains for studying charge exchange is the problem of electron terms in the field of two stationary Coulomb centers (TCC) of charges Z and Z′ separated by a distance R. It presents an intriguing atomic physics: the terms can have crossings and quasi crossings. These intrinsic features of the TCC problem also manifest in different areas of physics, such as plasma spectroscopy: a quasi crossing of the TCC terms, by enhancing charge exchange, can result in an unusual structure (a dip) in the spectral line profile emitted by a Z-ion from a plasma consisting of both Z- and Z′-ions, as was shown theoretically and experimentally. Before the year 2000, the paradigm was that the preceding sophisticated features of the TCC problem and its flourishing applications were inherently quantum phenomena. In 2000, a purely classical description of the crossings of energy terms was presented. In the present paper we study the effect of an electric field (along the internuclear axis) on circular Rydberg states of the TCC system. We provide analytical results for strong fields, as well as numerical results for moderate fields. We show that the electric field has several effects. First, it leads to the appearance of an extra energy term: the fourth classical energy term — in addition to the three classical energy terms at zero field. Second, but more importantly, the electric field creates additional crossings of these energy terms. We show that some of these crossings significantly enhance charge exchange, while other crossings enhance the ionization of the Rydberg quasi molecule.

Multiphoton ionization of H2+ in the perturbative regime

Multiphoton ionization of the H 2+ hydrogen molecular ion at fixed internuclear distance is investigated in the lowest order perturbation theory (LOPT). The parallel and perpendicular orientations between the polarization laser vector of the electric field and the H 2+ internuclear axis direction are considered. We calculate the generalized cross sections for the N = 2 to N = 6 photon ionization processes and we identify in each case the intermediate-state resonances. We show the efficiency of our method to describe resonance structures with high-energy resolution.

EXOTIC MOLECULAR IONS (HeH)2+ AND ${\rm He}_2^{3+}$ IN A STRONG MAGNETIC FIELD: LOW-LYING STATES

The Coulombic systems (αpe) and (ααe), (αppe), (ααpe) and ( Li 3+ Li 3+e) placed in a magnetic field B ≳ 1011 G are studied. It is demonstrated a theoretical existence of the exotic ion ( He H )2+ for B ≳ 5 × 1012 G in parallel configuration (the magnetic field is directed along internuclear axis) as optimal as well as its excited states 1π, 1δ. As for the exotic ion [Formula: see text] it is shown that in spite of strong electrostatic repulsion of α-particles this ion can also exist for B ≳ 100 a.u. (= 2.35 × 1011 G ) in parallel configuration as optimal in the states 1σg (ground state), 1πu, 1δg. Upon appearance both ions are unstable towards dissociation with He + in the final state but with very large lifetime. However, at B ≳ 10000 a.u. , the ion ( He H )2+ becomes stable, while at B ≳ 1000 a.u. , the ion [Formula: see text] becomes stable. For both ions the vibrational and rotational energies are calculated. With a magnetic field growth, both exotic ions become more and more tightly bound and compact, their lowest rotational and vibrational energies grow drastically. At the edge of applicability of nonrelativistic approximation, B ~ 4.414 × 1013 G , there are indications that three more exotic linear ions ( H – He – H )3+, ( He – H – He )4+ and even [Formula: see text] in parallel configuration may also occur.

COULOMB SYSTEMS IN A STRONG MAGNETIC FIELD

A study of what would the atomic–molecular physics be in an external strong magnetic field is presented. Emphasis is made on one-electron systems which seem the most bound, since two- and more-electron systems are weakly bound due to their maximal total spin nature. We demonstrate that the Coulombic systems (αpe) and (ααe) placed in (astro-physically relevant) magnetic fields B>1011 G become bound. It manifests a theoretical existence of the exotic ions ( HeH )2+ and [Formula: see text] with parallel configuration (the magnetic field is directed along the internuclear axis) as optimal. Both ions are unstable towards dissociation but do have very large lifetimes. At B>1000 a.u. the ion [Formula: see text] becomes stable and even becomes the most stable among one-electron ions made from protons and/or α-particles. A table of one-electron atomic–molecular systems which may exist in a strong magnetic field is given.