The Experts below are selected from a list of 123 Experts worldwide ranked by ideXlab platform
Klaus Eichhorn - One of the best experts on this subject based on the ideXlab platform.
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Determination of the Anharmonicity Constant of GaAs by means of the Bijvoet relation of the weak (666) reflection
Acta Crystallographica Section B-structural Science, 1993Co-Authors: Ullrich Pietsch, Katrin Paschke, Klaus EichhornAbstract:As a result of the influence of anomalous dispersion the weak (hhh) and (hhh) reflections of the zinc blende structure differ from each other. At large scattering vectors this difference, described by the Bijvoet relation B, depends solely on the size of the anharmonic force Constant β. It can be determined by measuring B near the K-absorption edge of any constituent. This experiment was performed for the (666) and (666) reflections of GaAs between λ=0.90 and 0.97 A using synchrotron radiation. Outside the extended X-ray absorption fine-structure spectroscopy region the integrated intensities decrease in a different manner with increasing λ for both reflections measured at «umweganregung» free azimuthal positions
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Determination of the Anharmonicity Constant of GaAs by means of the Bijvoet-relation of the weak (666) reflection
Acta Crystallographica Section A, 1993Co-Authors: Ullrich Pietsch, Katrin Paschke, Klaus EichhornAbstract:As a result of the influence of anomalous dispersion the weak (hhh) and (hhh) reflections of the zinc blende structure differ from each other. At large scattering vectors this difference, described by the Bijvoet relation B, depends solely on the size of the anharmonic force Constant /3. It can be determined by measuring B near the K-absorption edge of any constituent. This experiment was performed for the (666) and (666) reflections of GaAs between A = 0.90 and 0.97 A, using synchrotron radiation. Outside the extended X-ray absorption fine-structure spectroscopy region the integrated intensities decrease in a different manner with increasing A for both reflections measured at 'umweganregung' free azimuthal positions. Under the assumption of/3Oa = --/3As and using the measured wavelength dependence of B, the Anharmonicity Constant is evaluated to /3 = -1.75 (0.15) × 10-17j -3 which is nearly the same as that for germanium.
Mitsuo Tasumi - One of the best experts on this subject based on the ideXlab platform.
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Assignment and Anharmonicity analysis of overtone and combination bands observed in the resonance Raman spectra of carotenoids
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1994Co-Authors: Hiromi Okamoto, Yaeko Sekimoto, Mitsuo TasumiAbstract:Abstract The resonance Raman spectra of all- trans carotenoids have been observed in the region of 5000-500 cm −1 for samples in glassy solution at 77 K and in the in vivo state at room temperature. Prominent bands in the wavenumber region higher than 2000 cm −1 are assigned to either overtones or combinations of three modes due to skeletal stretches and the CH 3 in-plane rock. From the wavenumbers of the observed Raman bands, Anharmonicity Constants for these three modes (including cross-term Constants) are obtained. It is found that, for each carotenoid studied, the cross-term Anharmonicity Constant between the CC and CC stretches is significantly larger than the other Anharmonicity Constants.
Barbara Kirchner - One of the best experts on this subject based on the ideXlab platform.
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Anharmonicity of Vibrational Modes in Hydrogen Chloride-Water Mixtures.
Journal of chemical theory and computation, 2019Co-Authors: Eva Perlt, Sarah A Berger, Anne-marie Kelterer, Barbara KirchnerAbstract:A thorough analysis of molecular vibrations in the binary system hydrogen chloride/water is presented considering a set of small mixed and pure clusters. In addition to the conventional normal-mode analysis based on the diagonalization of the Hessian, anharmonic frequencies were obtained from the perturbative VPT2 and PT2-VSCF method using hybrid density functional theory. For all normal modes, potential energy curves were modeled by displacing the atoms from the minimum geometry along the normal mode vectors. Three model potentials, a harmonic potential, a Morse potential, and a fourth order polynomial, were applied to fit these curves. From these data, it was possible not only to characterize distinct vibrations as mainly harmonic, anharmonic, or involving higher order terms but also to extract force Constants, k, and Anharmonicity Constants, xe. By investigating all different types of intramolecular vibrations including covalent stretching or bending vibrations and intermolecular vibrations such as librations, we could demonstrate that while vibrational frequencies can be obtained applying scaling factors to harmonic results, useful Anharmonicity Constants cannot be predicted in such a way and the usage of more elaborate vibrational methods is necessary. For each particular type of molecular vibration, we could however determine a relationship between the wavenumber or wavenumber shift and the Anharmonicity Constant, which allows us to estimate mode dependent Anharmonicity Constants for larger clusters in the future.
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Anharmonicity of Vibrational Modes in Hydrogen Chloride–Water Mixtures
2019Co-Authors: Eva Perlt, Sarah A Berger, Anne-marie Kelterer, Barbara KirchnerAbstract:A thorough analysis of molecular vibrations in the binary system hydrogen chloride/water is presented considering a set of small mixed and pure clusters. In addition to the conventional normal-mode analysis based on the diagonalization of the Hessian, anharmonic frequencies were obtained from the perturbative VPT2 and PT2-VSCF method using hybrid density functional theory. For all normal modes, potential energy curves were modeled by displacing the atoms from the minimum geometry along the normal mode vectors. Three model potentials, a harmonic potential, a Morse potential, and a fourth order polynomial, were applied to fit these curves. From these data, it was possible not only to characterize distinct vibrations as mainly harmonic, anharmonic, or involving higher order terms but also to extract force Constants, k, and Anharmonicity Constants, xe. By investigating all different types of intramolecular vibrations including covalent stretching or bending vibrations and intermolecular vibrations such as librations, we could demonstrate that while vibrational frequencies can be obtained applying scaling factors to harmonic results, useful Anharmonicity Constants cannot be predicted in such a way and the usage of more elaborate vibrational methods is necessary. For each particular type of molecular vibration, we could however determine a relationship between the wavenumber or wavenumber shift and the Anharmonicity Constant, which allows us to estimate mode dependent Anharmonicity Constants for larger clusters in the future
Ullrich Pietsch - One of the best experts on this subject based on the ideXlab platform.
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Determination of the Anharmonicity Constant of GaAs by means of the Bijvoet relation of the weak (666) reflection
Acta Crystallographica Section B-structural Science, 1993Co-Authors: Ullrich Pietsch, Katrin Paschke, Klaus EichhornAbstract:As a result of the influence of anomalous dispersion the weak (hhh) and (hhh) reflections of the zinc blende structure differ from each other. At large scattering vectors this difference, described by the Bijvoet relation B, depends solely on the size of the anharmonic force Constant β. It can be determined by measuring B near the K-absorption edge of any constituent. This experiment was performed for the (666) and (666) reflections of GaAs between λ=0.90 and 0.97 A using synchrotron radiation. Outside the extended X-ray absorption fine-structure spectroscopy region the integrated intensities decrease in a different manner with increasing λ for both reflections measured at «umweganregung» free azimuthal positions
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Determination of the Anharmonicity Constant of GaAs by means of the Bijvoet-relation of the weak (666) reflection
Acta Crystallographica Section A, 1993Co-Authors: Ullrich Pietsch, Katrin Paschke, Klaus EichhornAbstract:As a result of the influence of anomalous dispersion the weak (hhh) and (hhh) reflections of the zinc blende structure differ from each other. At large scattering vectors this difference, described by the Bijvoet relation B, depends solely on the size of the anharmonic force Constant /3. It can be determined by measuring B near the K-absorption edge of any constituent. This experiment was performed for the (666) and (666) reflections of GaAs between A = 0.90 and 0.97 A, using synchrotron radiation. Outside the extended X-ray absorption fine-structure spectroscopy region the integrated intensities decrease in a different manner with increasing A for both reflections measured at 'umweganregung' free azimuthal positions. Under the assumption of/3Oa = --/3As and using the measured wavelength dependence of B, the Anharmonicity Constant is evaluated to /3 = -1.75 (0.15) × 10-17j -3 which is nearly the same as that for germanium.
Hiromi Okamoto - One of the best experts on this subject based on the ideXlab platform.
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Assignment and Anharmonicity analysis of overtone and combination bands observed in the resonance Raman spectra of carotenoids
Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 1994Co-Authors: Hiromi Okamoto, Yaeko Sekimoto, Mitsuo TasumiAbstract:Abstract The resonance Raman spectra of all- trans carotenoids have been observed in the region of 5000-500 cm −1 for samples in glassy solution at 77 K and in the in vivo state at room temperature. Prominent bands in the wavenumber region higher than 2000 cm −1 are assigned to either overtones or combinations of three modes due to skeletal stretches and the CH 3 in-plane rock. From the wavenumbers of the observed Raman bands, Anharmonicity Constants for these three modes (including cross-term Constants) are obtained. It is found that, for each carotenoid studied, the cross-term Anharmonicity Constant between the CC and CC stretches is significantly larger than the other Anharmonicity Constants.