Dissociative electron attachment to the H2O molecule. I. Complex-valued potential-energy surfaces for the 2B1, 2A1, and 2B2 metastable states of the water anion

We present the results of calculations defining global, three-dimensional representations of the complex-valued potential-energy surfaces of the doublet B1, doublet A1, and doublet B2 metastable states of the water anion that underlie the physical process of dissociative electron attachment to water. The real part of the resonance energies is obtained from configuration-interaction calculations performed in a restricted Hilbert space, while the imaginary part of the energies (the widths) is derived from complex Kohn scattering calculations. A diabatization is performed on the 2A1 and 2B2 surfaces, due to the presence of a conical intersection between them. We discuss the implications that the shapes of the constructed potential-energy surfaces will have upon the nuclear dynamics of dissociative electron attachment to H2O. This work originally appeared as Phys Rev A 75, 012710 (2007). Typesetting errors in the published version have been corrected here.Comment: Corrected version of PRA 75, 012710 (2007

Resonant ion-pair formation in electron recombination with HF^+

The cross section for resonant ion-pair formation in the collision of low-energy electrons with HF^+ is calculated by the solution of the time-dependent Schrodinger equation with multiple coupled states using a wave packet method. A diabatization procedure is proposed to obtain the electronic couplings between quasidiabatic potentials of ^1Sigma^+ symmetry for HF. By including these couplings between the neutral states, the cross section for ion-pair formation increases with about two orders of magnitude compared with the cross section for direct dissociation. Qualitative agreement with the measured cross section is obtained. The oscillations in the calculated cross section are analyzed. The cross section for ion-pair formation in electron recombination with DF^+ is calculated to determine the effect of isotopic substitution.Comment: 12 pages, 12 figure

Theoretical studies of photoexcitation and ionization in H_2O

Theoretical studies are reported of the complete dipole excitation and ionization spectrum in H_2O employing Franck–Condon and static‐exchange approximations. Large Cartesian Gaussian basis sets are used to represent the required discrete and continuum electronic eigenfunctions at the ground‐state equilibrium geometry, and previously devised moment‐theory techniques are employed in constructing the continuum oscillator‐strength densities from the calculated spectra. Detailed comparisons are made of the calculated excitation and ionization profiles with recent experimental photoabsorption studies and corresponding spectral assignments, electron impact–excitation cross sections, and dipole (e, 2e)/(e, e+ion) and synchrotron‐radiation studies of partial‐channel photoionization cross sections. The various calculated excitation series in the outer‐valence (1b(^−1)_1, 3a(^−1)_1, 1b(^−1)_2) region are found to include contributions from valence‐like 2b_2 (σ*) and 4a_1(γ*) virtual orbitals, as well as appropriate nsa_1, npa_1, nda_1, npb_1, npb_2, ndb_1, ndb_2, and nda_2 Rydberg states. Transition energies and intensities in the ∼7 to 19 eV interval obtained from the present studies are seen to be in excellent agreement with the measured photoabsorption cross section, and to provide a basis for detailed spectral assignments. The calculated (1b(^−1)_1)X(^ 2)B_1, (3a_1(^−1))^2A_1, and (1b_2(^−1))(^2)B_2 partial‐channel cross sections are found to be largely atomic‐like and dominated by 2p→kd components, although the 2b_2(σ*) orbital gives rise to resonance‐like contributions just above threshold in the 3a_1→kb_2 and 1b_2→kb_2 channels. It is suggested that the latter transition couples with the underlying 1b_1→kb_1 channel, accounting for a prominent feature in the recent high‐resolution synchrotron‐radiation measurements. When this feature is taken into account, the calculations of the three outer‐valence channels are in excellent accord with recent synchrotron‐radiation and dipole (e, 2e) photoionization cross‐sectional measurements. The calculated inner‐valence (2a_1(^−1)) cross section is also in excellent agreement with corresponding measured values, although proper account must be taken of the appropriate final‐state configuration‐mixing effects that give rise to a modest failure of the Koopmans approximation, and to the observed broad PES band, in this case. Finally, the origins of the various spectral features present in the measured 1a_1 oxygen K‐edge electron energy‐loss profile in H_2O are seen to be clarified fully by the present calculations

Biomimetic sulfide oxidation by the means of immobilized Fe(III)-5,10,15,20-tetrakis(pentafluorophenyl)porphin under mild experimental conditions

This paper describes the oxidation of inorganic sulfide to sulfate, minimizing the formation of elemental sulfur. The described catalytic reaction uses dilute hydrogen peroxide at nearly neutral pH values in the presence of a bioinspired, heterogenized, and commercial ferriporphin. A substantial increase of the percentage of sulfide converted to sulfate is obtained in comparison with the yields obtained when working with hydrogen peroxide alone. The biomimetic catalyst also proved to be a much more efficient catalyst than horseradish peroxidase. Accordingly, it could be suitable for large-scale applications. Further studies are in progress to drive sulfate yields up to nearly quantitative

Representation of a complex Green function on a real basis: I. General Theory

When the Hamiltonian of a system is represented by a finite matrix, constructed from a discrete basis, the matrix representation of the resolvent covers only one branch. We show how all branches can be specified by the phase of a complex unit of time. This permits the Hamiltonian matrix to be constructed on a real basis; the only duty of the basis is to span the dynamical region of space, without regard for the particular asymptotic boundary conditions that pertain to the problem of interest.Comment: about 40 pages with 5 eps-figure

An echocardiographic-confirmed case of atrial myxoma causing cerebral embolic ischemic stroke: a case report

A myxoma is the most common primary tumor of the heart. It has been reported as the source of a cardiogenic embolism. Therefore, it is important for clinicians to detect the myxoma early via echocardiography to prevent complications, such as syncope, sudden death, and cerebral embolic ischemic stroke. This report presents the case of a 54-year-old female whose clinical manifestation of atrial myxoma was an ischemic stroke. Atrial myxoma was later confirmed as the cause of her symptoms via transesophageal echocardiography

Dissociative electron attachment to the H2O molecule. II. Nuclear dynamics on coupled electronic surfaces within the local complex potential model

We report the results of a first-principles study of dissociative electron attachment to H2O. The cross sections are obtained from nuclear dynamics calculations carried out in full dimensionality within the local complex potential model by using the multi-configuration time-dependent Hartree method. The calculations employ our previously obtained global, complex-valued, potential-energy surfaces for the three (doublet B1, doublet A1, and doublet B2) electronic Feshbach resonances involved in this process. These three metastable states of H2O- undergo several degeneracies, and we incorporate both the Renner-Teller coupling between the B1 and A1 states as well as the conical intersection between the A1 and B2 states into our treatment. The nuclear dynamics are inherently multidimensional and involve branching between different final product arrangements as well as extensive excitation of the diatomic fragment. Our results successfully mirror the qualitative features of the major fragment channels observed, but are less successful in reproducing the available results for some of the minor channels. We comment on the applicability of the local complex potential model to such a complicated resonant system.Comment: Corrected version of Phys Rev A 75, 012711 (2007

Pseudospectral Calculation of the Wavefunction of Helium and the Negative Hydrogen Ion

We study the numerical solution of the non-relativistic Schr\"{o}dinger equation for two-electron atoms in ground and excited S-states using pseudospectral (PS) methods of calculation. The calculation achieves convergence rates for the energy, Cauchy error in the wavefunction, and variance in local energy that are exponentially fast for all practical purposes. The method requires three separate subdomains to handle the wavefunction's cusp-like behavior near the two-particle coalescences. The use of three subdomains is essential to maintaining exponential convergence. A comparison of several different treatments of the cusps and the semi-infinite domain suggest that the simplest prescription is sufficient. For many purposes it proves unnecessary to handle the logarithmic behavior near the three-particle coalescence in a special way. The PS method has many virtues: no explicit assumptions need be made about the asymptotic behavior of the wavefunction near cusps or at large distances, the local energy is exactly equal to the calculated global energy at all collocation points, local errors go down everywhere with increasing resolution, the effective basis using Chebyshev polynomials is complete and simple, and the method is easily extensible to other bound states. This study serves as a proof-of-principle of the method for more general two- and possibly three-electron applications.Comment: 23 pages, 20 figures, 2 tables, Final refereed version - Some references added, some stylistic changes, added paragraph to matrix methods section, added last sentence to abstract

Environmentally safe ZVI/ZnS-based polymer composite for lindane degradation in water: Assessment of photocatalytic activity and eco-toxicity

Monolithic composite aerogel based on a photocatalytic system, constituted by Fe0 (ZVI) coupled with ZnS (FZ), embedded into syndiotactic polystyrene (sPS) matrix was used, for the first time, in the lindane degradation under UV light. The content of FZ photocatalyst inside the monolithic composite aerogel (FZsPS) composite was 3 wt%. FESEM images of FZsPS indicate that the FZ photocatalyst is well dispersed in the polymer matrix. EDS analyses and temperature-programmed reduction (TPR-H2) measurements revealed an interpenetrated structure of the ZVI and ZnS phases as well the presence of some iron in an oxidized form. Photocatalytic activity data showed that in presence FZsPS aerogel, the almost complete lindane degradation was achieved after only 30 min of UV irradiation time. FZsPS was also effective in the lindane mineralization since a TOC removal of about 94 % was detected after 180 min of treatment time. Remarkably, based on the toxicity evaluation on Artemia fran-ciscana, while the bare FZ photocatalyst showed significant toxicity per se, no toxicity or genotoxicity was found in the water treated with the FZsPS composite system where FZ is immobilized into the sPS aerogel matrix. Therefore the proposed composite photocatalyst can be considered as a model for a strategy to eliminate the environmental impact of catalysts that would otherwise be harmful to water