ABSTRACT The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and t... more ABSTRACT 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.
ABSTRACT Optical absorption and emission measurements of Cu^2+ as a substitutional impurity in cu... more ABSTRACT Optical absorption and emission measurements of Cu^2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The ^2D term of Cu^2+ is split by a crystal field of tetrahedral symmetry into a ^2 Gamma5 orbital triplet and a ^2 Gamma3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu^2+ and within the ^2Gamma5 ground state in ZnTe:Cu^2+. The theoretical model is based on crystal field theory and includes the spin-orbit interaction and a dynamic Jahn-Teller interaction between the electronic ^2Gamma5 states and a transverse acoustic phonon of Gamma5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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.
ABSTRACT The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and t... more ABSTRACT 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.
ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cub... more ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The 2D term of Cu2+ is split by a crystal field of tetrahedral symmetry into a 2Γ5 orbital triplet and a 2Γ3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu2+ and within the 2Γ5 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 2Γ5 states and a transverse acoustic phonon of Γ5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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 Δ=5990.6 cm-1, the spin-orbit coupling constants λ1=-667 cm-1 and λ2=-830 cm-1, the phonon energy ħω=73.5 cm-1, and the Jahn-Teller stabilization energy EJT=474.5 cm-1. The corresponding parameters in ZnTe are Δ=6000 cm-1, λ1=-888 cm-1, λ2=-830 cm-1, ħω=38.8 cm-1, and EJT=468.5 cm-1.
The 5D terms of Fe2+ and Cr2+ in the tetrahedral potential at cation sites in II–VI compounds spl... more The 5D 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 triplet 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.
ABSTRACT A theoretical study of the isotopic-mass dependence of the internal transitions of Fe^2+... more ABSTRACT A theoretical study of the isotopic-mass dependence of the internal transitions of Fe^2+ at a cation site in a cubic zinc-blende semiconductor is presented. The model used is based on crystal-field theory, including spin-orbit and spin-spin interactions and a dynamic Jahn-Teller coupling between the ^5 Gamma5 excited manifold of Fe^2+ and a phonon of Gamma5 symmetry. The effect of the dynamic Jahn-Teller interaction on the local vibronic states is calculated as a function of the isotopic mass using a model similar to that of Colignon et al. (D. Colignon, E. Kartheuser, S. Rodriguez, and M. Villeret, Phys. Rev. B 51), 4849 (1995). The theoretical results are compared with the observed isotopic shifts (K. Pressel, K. Thonke, A. Dörnen, and G. Pensel, Phys. Rev. B 43), 2239 (1991). of the zero-phonon line in InP:Fe^2+ originating from optical transitions between the vibronic Gamma1 ground state and Gamma5 excited states. Work supported by NSF Grant No. DMR 93-03186, The Nuffield Science Foundation (U.K.) and by the North Atlantic Treaty Organization (Research Grant No. 960666).
A theoretical study of optical absorption and emission measurements of Fe2+ as a substitutional i... 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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.
ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cub... more ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The 2D term of Cu2+ is split by a crystal field of tetrahedral symmetry into a 2Γ5 orbital triplet and a 2Γ3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu2+ and within the 2Γ5 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 2Γ5 states and a transverse acoustic phonon of Γ5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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 Δ=5990.6 cm-1, the spin-orbit coupling constants λ1=-667 cm-1 and λ2=-830 cm-1, the phonon energy ħω=73.5 cm-1, and the Jahn-Teller stabilization energy EJT=474.5 cm-1. The corresponding parameters in ZnTe are Δ=6000 cm-1, λ1=-888 cm-1, λ2=-830 cm-1, ħω=38.8 cm-1, and EJT=468.5 cm-1.
ABSTRACT The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and t... more ABSTRACT 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.
ABSTRACT Optical absorption and emission measurements of Cu^2+ as a substitutional impurity in cu... more ABSTRACT Optical absorption and emission measurements of Cu^2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The ^2D term of Cu^2+ is split by a crystal field of tetrahedral symmetry into a ^2 Gamma5 orbital triplet and a ^2 Gamma3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu^2+ and within the ^2Gamma5 ground state in ZnTe:Cu^2+. The theoretical model is based on crystal field theory and includes the spin-orbit interaction and a dynamic Jahn-Teller interaction between the electronic ^2Gamma5 states and a transverse acoustic phonon of Gamma5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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.
ABSTRACT The Jovian aurora exhibits bright emissions mainly due the bright Lyman-alpha line and t... more ABSTRACT 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.
ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cub... more ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The 2D term of Cu2+ is split by a crystal field of tetrahedral symmetry into a 2Γ5 orbital triplet and a 2Γ3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu2+ and within the 2Γ5 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 2Γ5 states and a transverse acoustic phonon of Γ5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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 Δ=5990.6 cm-1, the spin-orbit coupling constants λ1=-667 cm-1 and λ2=-830 cm-1, the phonon energy ħω=73.5 cm-1, and the Jahn-Teller stabilization energy EJT=474.5 cm-1. The corresponding parameters in ZnTe are Δ=6000 cm-1, λ1=-888 cm-1, λ2=-830 cm-1, ħω=38.8 cm-1, and EJT=468.5 cm-1.
The 5D terms of Fe2+ and Cr2+ in the tetrahedral potential at cation sites in II–VI compounds spl... more The 5D 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 triplet 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.
ABSTRACT A theoretical study of the isotopic-mass dependence of the internal transitions of Fe^2+... more ABSTRACT A theoretical study of the isotopic-mass dependence of the internal transitions of Fe^2+ at a cation site in a cubic zinc-blende semiconductor is presented. The model used is based on crystal-field theory, including spin-orbit and spin-spin interactions and a dynamic Jahn-Teller coupling between the ^5 Gamma5 excited manifold of Fe^2+ and a phonon of Gamma5 symmetry. The effect of the dynamic Jahn-Teller interaction on the local vibronic states is calculated as a function of the isotopic mass using a model similar to that of Colignon et al. (D. Colignon, E. Kartheuser, S. Rodriguez, and M. Villeret, Phys. Rev. B 51), 4849 (1995). The theoretical results are compared with the observed isotopic shifts (K. Pressel, K. Thonke, A. Dörnen, and G. Pensel, Phys. Rev. B 43), 2239 (1991). of the zero-phonon line in InP:Fe^2+ originating from optical transitions between the vibronic Gamma1 ground state and Gamma5 excited states. Work supported by NSF Grant No. DMR 93-03186, The Nuffield Science Foundation (U.K.) and by the North Atlantic Treaty Organization (Research Grant No. 960666).
A theoretical study of optical absorption and emission measurements of Fe2+ as a substitutional i... 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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 icons/Journals/Common/Gamma" ALT="Gamma" ALIGN="TOP"/> 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.
ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cub... more ABSTRACT Optical absorption and emission measurements of Cu2+ as a substitutional impurity in cubic ZnS and ZnTe are analyzed by means of an electron-phonon coupling model. The 2D term of Cu2+ is split by a crystal field of tetrahedral symmetry into a 2Γ5 orbital triplet and a 2Γ3 orbital doublet. Optical transitions have been observed between these two multiplets in ZnS:Cu2+ and within the 2Γ5 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 2Γ5 states and a transverse acoustic phonon of Γ5 symmetry. Starting from the ten spin-orbit wave functions appropriate to the orbital triplet and doublet 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 Δ=5990.6 cm-1, the spin-orbit coupling constants λ1=-667 cm-1 and λ2=-830 cm-1, the phonon energy ħω=73.5 cm-1, and the Jahn-Teller stabilization energy EJT=474.5 cm-1. The corresponding parameters in ZnTe are Δ=6000 cm-1, λ1=-888 cm-1, λ2=-830 cm-1, ħω=38.8 cm-1, and EJT=468.5 cm-1.
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Papers by David Colignon