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High-Frequency Integral Equation Solver for 3-D Wave Scattering Around Convex Obstacles Geuzaine, Christophe ; ; V Sabariego, Ruth et al in Proceedings of 6ème Conférence Européenne sur les Méthodes Numériques en Electromagnétisme (NUMELEC2008) (2008) We present a numerical method for the computation of wave scattering by convex three-dimensional obstacles, which exhibits a bounded computational complexity for arbitrarily high frequencies. The method ... [more ▼] We present a numerical method for the computation of wave scattering by convex three-dimensional obstacles, which exhibits a bounded computational complexity for arbitrarily high frequencies. The method is based on a combination of a high-frequency ansatz for the unknown density in a boundary integral formulation of the problem, and an extension of the ideas of the method of stationary phase to allow for the efﬁcient integration of oscillatory functions. The method builds upon the ideas proposed in [2] and [1]. [less ▲] Detailed reference viewed: 157 (31 ULg)The effect of electron-phonon interaction in iron-doped III-V cubic semiconductors Colignon, David ; Kartheuser, Eduard ; in Journal of Physics : Condensed Matter (2000), 12(12), 2691-2699 A theoretical study of optical absorption and emission measurements of Fe2+ as a substitutional impurity in InP and GaP is presented. A new interpretation of the low-temperature absorption spectrum is ... [more ▼] A theoretical study of optical absorption and emission measurements of Fe2+ as a substitutional impurity in InP and GaP is presented. A new interpretation of the low-temperature absorption spectrum is proposed based on a weak Jahn-Teller interaction between the electronic excited states and a local gap mode of Gamma(5) symmetry. The model also includes the crystal potential, hybridization with the orbitals of the ligands of the host crystal, spin-orbit interaction and a weak dynamic Jahn-Teller coupling of the orbital ground state of Fe2+ with transverse acoustic phonons of Gamma(3) symmetry. The theoretical model describes with good accuracy the measured positions and relative intensities of the spectral lines. In addition, the mass dependence of the local gap mode of Gamma(5) symmetry reproduces the general features of the fine structures associated with the isotopic shifts of the zero-phonon line and the contribution to the isotopic shifts arising from the difference in zero-point energy between the initial and final states of the transition is evaluated. [less ▲] Detailed reference viewed: 52 (6 ULg)FUV spectroscopy of the H_2 emission in the Jovian aurora: model update and results Gérard, Jean-Claude ; ; Colignon, David et al in Bulletin of the American Astronomical Society (1998, September 01) The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and to radiation from excited singlet states to the ground electronic state extending from 800 to 1600 Angstroms. Above ... [more ▼] The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and to radiation from excited singlet states to the ground electronic state extending from 800 to 1600 Angstroms. Above 1200 Angstroms, the molecular spectrum is dominated by the Lyman (B-X) bands and continuum and the Werner (C-X) bands. These transitions have been observed with the Goddard High Resolution Spectrometer (GHRS) and the Space Telescope Imaging Spectrometer (STIS) at various spectral and spatial resolutions. To analyze these spectra, a model synthetic auroral spectrum has been constructed and applied to the analysis of the ro-vibrational temperature of H_2 and a search for non-H_2 emission features. It has been recently updated to include the latest singlet state excitation and cascading cross sections, self-absorption in optically thick lines and to account for the energy distribution of the secondary electrons which cause additional excitation. We illustrate these effects in a few study cases and apply the model to high resolution (0.5 Angstroms) GHRS spectra and low resolution STIS spectra of the entire H_2 spectrum at wavelengths longer than Lyman-alpha. We determine the methane column overlying the auroral emission peak and find that a better fit is obtained with additional absorption by acetylene. [less ▲] Detailed reference viewed: 26 (4 ULg)Dynamic Jahn-Teller interaction with Gamma(5) phonons in the ground state of Cu2+ in cubic II-VI semiconductors Colignon, David ; ; Kartheuser, Eduard et al in Physical Review. B : Condensed Matter (1998), 57(20), 12932-12938 Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe rue analyzed by means of an electron-phonon coupling model. The D-2 term of Cu2+ is split by a ... [more ▼] Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe rue analyzed by means of an electron-phonon coupling model. The D-2 term of Cu2+ is split by a crystal field of tetrahedral symmetry into a (2) Gamma(5) orbital triplet and a (2) Gamma(3) orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu2+ and within the (2) Gamma(5) ground state in ZnTe:Cu2+. The theoretical model is based on crystal-field theory and includes the spin-orbit interaction and a dynamic Jahn-Teller interaction between the electronic (2) Gamma(5) states and a transverse acoustic phonon of TI symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital tripler and doubler manifolds, the symmetry-adapted vibronic basis is constructed and used to diagonalize the Hamiltonian matrix. Phonon overtones up to n = 14 are included to ensure convergence of the energy eigenvalues. The measured positions and relative intensities of the spectral lines are described with good accuracy by the theoretical model, including covalency effects.. In ZnS, comparison between theory and experiment yields the following values of the physical parameters: the crystal-field splitting Delta = 5990.6 cm(-1), the spin-orbit coupling constants lambda(1) = -667 cm(-1) and lambda(2) = -830 cm(-1), the phonon energy h omega = 73.5 cm(-1), and the Jahn-Teller stabilization energy E-JT = 474.5 cm(-1) The corresponding parameters in ZnTe are Delta = 6000 cm(-1), lambda(1) = -888 cm(-1), lambda(2)= -830 cm(-1), h omega= 38.8 cm(-1), and E-JT= 468.5 cm(-1). [less ▲] Detailed reference viewed: 74 (5 ULg)Isotope splitting of the zero-phonon line of Fe2+ in cubic III-V semiconductors Colignon, David ; ; Kartheuser, Eduard et al in Solid State Communications (1998), 105(4), 205-209 A theoretical study of the isotopic-mass dependence of the internal transitions of Fe2+ at a cation site in a cubic zinc-blende semiconductor is presented. The model used is based on crystal-field theory ... [more ▼] A theoretical study of the isotopic-mass dependence of the internal transitions of Fe2+ at a cation site in a cubic zinc-blende semiconductor is presented. The model used is based on crystal-field theory and includes the spin-orbit interaction and a weak dynamic Jahn-Teller coupling between the (5) Gamma(5) excited manifold of Fe2+ and a local vibrational mode (LVM) of Gamma(5) symmetry. The mass dependence of the LVM frequency is described, in the harmonic approximation, within two different limits: the rigid-cage model and a molecular model. In the rigid-cage model, the Fe2+ ion undergoes a displacement but the rest of the lattice is fixed. In this case, a simple M-1/2 dependence of the frequency is obtained and the Jahn-Teller energy, E-JT, is independent of the mass. In the molecular model, the four nearest neighbors of the magnetic ion are allowed to move and the LVM then behaves as the Gamma(5) mode of a MX4 tetrahedral molecule leading to a more complicated dependence of the frequency on the isotopic mass and to a mass-dependence of E-JT. The theoretical results obtained with these two models are compared with the observed isotopic shifts of the zero-phonon lines in InP:Fe and GaP:Fe corresponding to an optical transition between the vibronic Gamma(1) ground state and the lowest Gamma(5) state originating from the (5) Gamma(5) excited orbital multiplet. A prediction of the isotopic shifts of the zero-phonon line in GaAs:Fe is also presented. (C) 1997 Elsevier Science Ltd. [less ▲] Detailed reference viewed: 35 (5 ULg)Near and far infrared transitions of Fe2+ in cubic II-VI semiconductors: Dynamic Jahn-Teller interaction Colignon, David ; Kartheuser, Eduard in Zeitschrift Fur Physikalische Chemie-International Journal Of Research In Physical Chemistry & Chemical Physics (1997), 201(Part 1), 119-126 Optical-absorption and emission measurements of doubly ionized iron in CdTe, ZnTe, ZnSe and ZnS have been analyzed by means of a vibronic coupling model. The model [1] is based on the crystal-field theory ... [more ▼] Optical-absorption and emission measurements of doubly ionized iron in CdTe, ZnTe, ZnSe and ZnS have been analyzed by means of a vibronic coupling model. The model [1] is based on the crystal-field theory, including spin-orbit and spin-spin interactions and Jahn-Teller couplings of the orbital doublet and triplet states of Fe2+ with overtones of phonons of Gamma(3) and Gamma(5) symmetries, respectively. Starting from the 25 spin-orbit wave functions appropriate to the orbital doublet and triplet manifolds, the symmetry-adapted vibronic basis is constructed and used to diagonalize the Hamiltonian matrix formed out of five blocks of symmetry Gamma(1), Gamma(2), Gamma(3), Gamma(4) and Gamma(5). Phonon overtones up to N=6 for the Gamma(3) phonon and up to N=10 for the Gamma(5) phonon were included to ensure convergence of the energy values and eigenfunction of the vibronic states. The available measured positions and relative intensities of the spectral lines in the near and far infrared are accounted for within the experimental accuracy. It is shown that the above mentioned iron based II-VI compounds (ZnS:Fe2+ excepted) exhibit a strong dynamic Jahn-Teller coupling of the upper orbital triplet state with phonons of Gamma(5) symmetry and that the spin-orbit interaction between the orbital doublet and triplet states of Fe2+ is essential to explain the data. [less ▲] Detailed reference viewed: 71 (6 ULg)Optical and magnetic properties of Fe2+ and Cr2+ in II-VI semiconductors: The Jahn-Teller effect Colignon, David ; Kartheuser, Eduard ; et al in Journal of Crystal Growth (1996), 159(1-4), 875-878 The D-5 terms of Fe2+ and Cr2+ in the tetrahedral potential at cation sites in II-VI compounds split into orbital doublet and triplet states. While in Cr2+ the orbital tripler has lower energy than the ... [more ▼] The D-5 terms of Fe2+ and Cr2+ in the tetrahedral potential at cation sites in II-VI compounds split into orbital doublet and triplet states. While in Cr2+ the orbital tripler has lower energy than the doublet the opposite is the case in Fe2+. Both ions have singlet ground states after the spin-orbit interaction is taken into account and, hence, both are Van Vleck paramagnets. The optical absorption spectra of Fe and Cr based materials differ and are explained on the basis of a dynamic Jahn-Teller effect in the former and a static one in the latter. These considerations permit us to explain the optical as well as the magnetic properties observed in these materials. [less ▲] Detailed reference viewed: 40 (2 ULg)Excitation spectrum of FE2+ in a tetrahedral potential - Dynamic Jahn-Teller effect Colignon, David ; Kartheuser, Eduard ; et al in Physical Review. B : Condensed Matter (1995) Detailed reference viewed: 33 (14 ULg) |
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