Zineb Felfli

Dramatic distortion of the 4d giant resonance by the C60 fullerene shell

The photoionization cross section for the endohedral Xe@C60 atom is investigated within the framework of representing the C60 by a delta-type potential. Results demonstrate that in Xe@C60, the 4d giant resonance is distorted significantly when compared with that of the isolated Xe atom. The reflection of the photoelectron waves by the C60 causes strong oscillations in the photoionization cross section resulting in the replacement of the Xe 4d giant resonance by four prominent peaks. The approximation of C60 by an infinitely thin real potential preserves reasonably well the sum rule for the 4d electrons but modifies the dipole polarizability of the 4d shell.

Novel mechanism for nanoscale catalysis

The interplay between Regge resonances and Ramsauer–Townsend minima in the electron elastic total cross sections for Au and Pd atoms along with their large electron affinities is proposed as the fundamental atomic mechanism responsible for the observed exceptional catalytic properties of Au nanoparticles and to explain why the combination Au–Pd possesses an even higher catalytic activity than Au or Pd separately when catalyzing H2O2, consistent with recent experiments. The investigation uses the recent complex angular momentum description of electron scattering from neutral atoms and the proposed mechanism in general.

Semiclassical approach to Regge poles trajectories calculations for nonsingular potentials: Thomas–Fermi type

A simple semiclassical approach, based on the investigation of anti-Stokes line topology, is presented for calculating Regge poles for nonsingular (Thomas–Fermi type) potentials, namely potentials with singularities at the origin weaker than order −2. The anti-Stokes lines for Thomas–Fermi potentials have a more complicated structure than those of singular potentials and require careful application of complex analysis. The explicit solution of the Bohr–Sommerfeld quantization condition is used to obtain approximate Regge poles. We introduce and employ three hypotheses to obtain several terms of the Regge pole approximation.Please note that the pdf of this article was replaced with a corrected version on 29 June 2004. Minor changes have been made to pages 6950–6953.

Simple method for electron affinity determination: results for Ca, Sr and Ce

Benchmarking the recently developed Regge-pole methodology for electron–atom elastic scattering on the most recently measured electron affinity (EA) of the Ca atom, we illustrate the predictive power of the methodology by calculating the binding energy of the tenuously bound negative ion Sr− and predicting the value of 0.61 eV for the binding energy of the ground state of the very complicated Ce− ion, with a g-orbital electron attachment, a shape resonance at 0.37 eV and a Ramsauer–Townsend minimum at about 0.09 eV. Our calculated EA value for the Ce atom favours the latest theoretical value rather than the measured one.

Generalized oscillator strengths for forward electron scattering

A simple analytical expression for calculating the generalized oscillator strengths for optically allowed atomic transitions in the forward direction is obtained. We found the correction to the first Born approximation by exploiting the analytical properties of the generalized oscillator strength function at small momentum transfers. A new procedure for experimental measurement of the differential cross sections for optically allowed transitions at small angles is proposed.

Normalization of the measured relative electron differential cross sections for 2 ^1Sigma+ and ^1Pi states of N2O

The measured relative electron differential cross sections (DCSs) for excitation of the 2 + and states of N2O (Marinkovic et al 1986 J. Phys. B: At. Mol. Phys. 19 2365) have been normalized through a recent forward scattering function for the generalized oscillator strength. Measurements were obtained at electron impact energies of 15, 20, 30, 50 and 80 eV, using the electron spectrometer with crossed electron-molecule beam arrangement. Measured data are corrected at and near zero scattering angles following the analytic behaviour of the momentum dispersion method. Absolute DCS values for the state are compared with the only available set of theoretical data, while for the 2 + state results are presented for the first time.

Low-energy electron elastic collision cross sections for ground and excited Tm, Lu and Hf atoms

Submitted for the DAMOP09 Meeting of The American Physical Society Electron Spectroscopy of Tenuously and Weakly Bound Negative Ions A.Z. MSEZANE, Z. FELFLI, Clark Atlanta University, D. SOKOLOVSKI, Queen’s University of Belfast, UK — We propose using very slow electron elastic collisions with atoms to identify their presence through observation of tenuously bound (impact energy, E<0.1 eV) and weakly bound (E<0.2 eV) negative ions, formed during the collisions. This could be important in identifying the presence of atoms in various environments. In an appropriate representation the characteristic very sharp resonances in electron-atom elastic total cross sections (TCSs) are enhanced significantly. Their positions yield the binding energies of the negative ions formed as Regge resonances, identified through the careful scrutiny of the complex angular momentum L. Two limiting curves determine the behavior as E→ 0. The TCSs for example Tm, Sr and Mn in the region of formation of their tenuously bound negative ions with Re L=2 electron attachment follow a Wigner threshold law determined by the lowest Regge trajectory. Resonances in TCSs for the group exemplified by Cd, Eu and Tc atoms forming weakly bound negative ions with Re L=3 electron attachment rest on a trajectory that approaches that for e-Ca scattering, with Re L=1 electron attachment. The calculations used the Regge-pole methodology with a Thomas-Fermi type potential [1, 2]. [1] D. Sokolovski et al, Phys. Rev. A76, 012705 (2007). [2] Z. Felfli et al, Phys. Rev. A78, 030703 (R) (2008). Supported by US DOE Office of Basic Energy Sciences. Z. Felfli Clark Atlanta University Date submitted: 26 Jan 2009 Electronic form version 1.4

Elastic scattering of slow electrons from Y, Ru, Pd, Ag and Pt atoms: search for nanocatalysts

Electron elastic scattering total cross sections (TCSs) for Y, Ru, Pd, Ag and Pt atoms are investigated in the electron impact energy range 0 ≤ E ≤ 7.0 eV. The complex angular momentum method that incorporates the electron–electron correlations and core-polarization interactions, crucial for the existence and stability of most negative ions, is used for the calculations. The TCSs for these atoms are found to be characterized by shape resonances (short-lived resonances), Ramsauer–Townsend minima and very sharp resonances (long-lived resonances) that correspond to the existence of stable bound states of the negative ions formed during the collision as Regge resonances. Using the configuration of the negative-ion resonances and Ramsauer–Townsend minima in the Au TCS as the benchmark for nanocatalysts, we conclude that the Y, Ru, Pd, Ag and Pt atoms represent excellent candidates for nanocatalysts individually or in various combinations. Calculated electron elastic TCSs for Y, Ru, Pd, Ag and Pt atoms are presented as illustrations.

Near-threshold resonances in electron elastic scattering cross sections for Au and Pt atoms: identification of electron affinities

The recent Regge-pole methodology has been employed together with a Thomas–Fermi type potential which incorporates the vital core-polarization interaction to investigate the near-threshold electron attachment in Au and Pt as Regge resonances. The resultant stable negative ion states are found to have the discernible characteristic of very small imaginary parts of the Regge poles, which translate into long-lived resonances. The near-threshold electron elastic total cross sections are characterized by multiple resonances from which we extract the electron affinity (EA) values through the scrutiny of the imaginary part of the relevant complex angular momentum. For the Au− and Pt− negative ions the extracted binding energies of 2.262 eV and 2.163 eV, respectively are in excellent agreement with the most recently measured EA values for Au and Pt. Ramsauer–Townsend minima, shape resonances and the Wigner threshold behaviour are identified in both Au− and Pt− ions.

Slow electron elastic scattering cross sections for In, Tl, Ga and At atoms

The complex angular momentum (CAM)-calculated, low-energy 0 ≤ E ≤ 5 eV electron elastic total cross section (TCS) for In is benchmarked through its recently measured electron affinity in Walter et al (2010 Phys. Rev. A 82 032507). The TCSs for Tl, Ga and At atoms are then calculated using the CAM method. From the dramatically sharp resonances in the TCSs, binding energies for Tl−, Ga− and At− negative ions formed during the collisions as Regge resonances are extracted and compared with the existing experimental and theoretical values.