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| 2. |
- Richard, C., et al.
(författare)
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New section of the HITRAN database: Collision-induced absorption (CIA)
- 2012
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Ingår i: Journal of Quantitative Spectroscopy & Radiative Transfer. - : Elsevier BV. - 0022-4073 .- 1879-1352. ; 113:11, s. 1276-1285
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Tidskriftsartikel (refereegranskat)abstract
- This paper describes the addition of Collision-Induced Absorption (CIA) into the HITRAN compilation. The data from different experimental and theoretical sources have been cast into a consistent format and formalism. The implementation of these new spectral data into the HITRAN database is invaluable for modeling and interpreting spectra of telluric and other planetary atmospheres as well as stellar atmospheres. In this implementation for HITRAN, CIAs of N-2, H-2, O-2, CO2, and CH4 due to various collisionally interacting atoms or molecules are presented. Some CIA spectra are given over an extended range of frequencies, including several H-2 overtone bands that are dipole-forbidden in the non-interacting molecules. Temperatures from tens to thousands of Kelvin are considered, as required, for example, in astrophysical analyses of objects, including cool white dwarfs, brown dwarfs. M dwarfs, cool main sequence stars, solar and extra-solar planets, and the formation of so-called first stars. (C) 2011 Elsevier Ltd. All rights reserved.
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| 3. |
- Abel, Martin, et al.
(författare)
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Collision-induced absorption by supermolecular complexes from a new potential energy and induced dipole surface, suited for calculations up to thousands of kelvin
- 2010
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Ingår i: 20th International Conference on Spectral Line Shapes. - Melville, NY : American Institute of Physics (AIP). - 9780735408456 ; , s. 251-257
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Konferensbidrag (refereegranskat)abstract
- Absorption by pairs of H2 molecules is an important opacity source in the atmospheres of the outer planets, and thus of special astronomical interest. The emission spectra of cool white dwarf stars differ significantly from the expected blackbody spectra, amongst other reasons due to absorption by H2-H2, H2-He, and H2-H collisional complexes in the stellar atmospheres. To model the radiative processes in these atmospheres, which have temperatures of several thousand kelvin, one needs accurate knowledge of the induced dipole (ID) and potential energy surfaces (PES) of such collisional complexes. These come from quantum-chemical calculations with the H2 bonds stretched or compressed far from equilibrium. Laboratory measurements of collision-induced (CI) absorption exist only at much lower temperature. For H2 pairs at room temperature, the calculated spectra of the rototranslational band, the fundamental band, and the first overtone match the experimental data very well. In addition, with the newly obtained IDS it became possible to reproduce the measurements in the far blue wing of the rototranslational spectrum of H2 at 77.5 K, as well as at 300 K. Similarly good agreement between theory and measurement is seen in the fundamental band of molecular deuterium at room temperature. Furthermore, we also show the calculated absorption spectra of H2-He at 600 K and of H2-H2 at 2,000 K, for which there are no experimental data for comparison
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| 4. |
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| 5. |
- Frommhold, Lothar, et al.
(författare)
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Infrared atmospheric emission and absorption by simple molecular complexes, from first principles
- 2010
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Ingår i: Molecular Physics. - : Informa UK Limited. - 0026-8976 .- 1362-3028. ; 108:17, s. 2265-2272
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Tidskriftsartikel (refereegranskat)abstract
- Quantum chemical methods are used to obtain the interaction-induced dipole surfaces (IDS) of complexes of two interacting (i.e. colliding) molecules, for example H2–H2, H2–He, etc., collisional complexes, along with their potential energy surfaces (PES). Eight H2 bond distances, from 0.942 to 2.801 bohr, are chosen for each H2 molecule to account for rotovibrational excitations. Rotovibrational matrix elements of these ID and PE surfaces are computed as necessary for the study of supermolecular (‘collision-induced’) absorption spectra of dense hydrogen gas, and of gaseous mixtures of hydrogen and helium, at temperatures up to several thousand kelvin and for frequencies from 0 to those of several H2 overtone bands. Rotovibrational state to state scattering calculations couple the collisional complex perturbatively to single photons. The absorption process causes rotovibrational transitions in one molecule, or simultaneous transitions in both molecules (when H2–H2 collisional complexes are considered). The spectral profiles of tens of thousands of such transitions are computed from first principles. Individual ‘lines’ are very broad so that they overlap substantially, forming a supermolecular quasi-continuum. The comparison of the computed collision-induced absorption (CIA) spectra with existing laboratory measurements at low temperatures (≤ 300 K) shows close agreement so that our results for higher temperatures, where laboratory experiments do not exist, may be used with confidence. Similar calculations of CIA spectra at high temperatures and frequencies are underway for other collisional systems (e.g. H2–H) of interest in astrophysical applications (e.g. ‘cool’ stellar atmospheres). Collision-induced Raman spectra (CIRS) have been similarly obtained; computed Raman spectra also compare favourably with existing laboratory measurements.
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| 6. |
- Gustafsson, Magnus, 1969, et al.
(författare)
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Roto-translational Raman spectra of pairs of hydrogen molecules from first principles
- 2009
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Ingår i: J. Chem. Phys.. - : AIP Publishing. ; 130
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the collision-induced, roto-translational, polarized, and depolarized Raman spectra of pairs of H2 molecules. The Schrödinger equation of H2–H2 scattering in the presence of a weak radiation field is integrated in the close-coupled scheme. This permits the accounting for the anisotropy of the intermolecular potential energy surface and thereby it includes mixing of polarizability components. The static polarizability invariants, trace and anisotropy, of two interacting H2 molecules were obtained elsewhere [Li et al., J. Chem. Phys. 126, 214302 (2007)] from first principles. Here we report the associated spherical tensor components which, along with the potential surface, are input in the calculation of the supramolecular Raman spectra. Special attention is paid to the interferences in the wings of the rotational S0(0) and S0(1) lines of the H2 molecule. The calculated Raman pair spectra show reasonable consistency with existing measurements of the polarized and depolarized Raman spectra of pairs of H2 molecules.
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| 7. |
- Li, Xiaoping, et al.
(författare)
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Collision-induced dipoles and polarizabilities of pairs of hydrogen molecules : Ab initio calculations and results from spherical tensor analysis
- 2012
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Ingår i: International Conference of Computational Methods in Sciences and Engineering 2009. - Melville, NY : American Institute of Physics (AIP). - 9780735411227 ; , s. 100-135
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Konferensbidrag (refereegranskat)abstract
- New ab initio results are reported for the interaction-induced changes in the dipole moments and polarizabilities of pairs of hydrogen molecules, computed using finite-field coupled-cluster methods in MOLPRO 2000 and GAMESS, with an aug-cc-pV5Z (spdf) basis set. Earlier work by X. Li, C. Ahuja, J. F. Harrison, and K. L. C. Hunt, J. Chem. Phys. 126, 214302 (2007), on collision-induced polarizabilities Δα has been extended with 170 additional geometrical configurations of the H2 pairs. In calculations of Δα, we have used a "random field" technique, with up to 120 different field strengths, having components that range from 0.001 to 0.01 a.u. Numerical tests show that the pair dipoles Δμ can be obtained accurately from calculations limited to 6 values of the field in each direction, so this approach has been used to compute Δμ by X. Li, K. L. C. Hunt, F. Wang, M. Abel, and L. Frommhold, Int. J. Spectroscopy 2010, 371201 (2010). We have evaluated the collision-induced dipoles of H2 pairs for 28 combinations of bond lengths (ranging from 0.942 a.u. to 2.801 a.u.), 7 intermolecular separations R, and 17 different relative orientations. In our work on Δα, the bond lengths are fixed at 1.449 a.u. Our results agree well with the previous ab initio work of W. Meyer, A. Borysow, and L. Frommhold, Phys. Rev. A 40, 6931 (1989), and of Y. Fu, C. G. Zheng and A. Borysow, J. Quant. Spectroscopy and Rad. Transfer, 67, 303 (2000)-where those data exist-for Δμ of H2 pairs. For Δα, our results agree well with the CCSD(T) results obtained by G. Maroulis, J. Phys. Chem. A 104, 4772 (2000) for two pair orientations and fixed R. The pair polarizability anisotropies also agree well with the small-basis self-consistent field results of D. G. Bounds, Mol. Phys. 38, 2099 (1979), although the trace of the polarizability differs by factors of 2 or more from Bounds' results. We have determined the expansion coefficients for Δμ and Δα, expressed as series in the spherical harmonics of the orientation angles of the intermolecular vector and of unit vectors along the molecular axes. The leading coefficients converge at long range to the predictions from perturbation theory, derived by J. E. Bohr and K. L. C. Hunt, J. Chem. Phys. 87, 3821 (1987); T. Bancewicz, W. G.az, and S. Kielich, Chem. Phys. 128, 321 (1988); and X. Li and K. L. C. Hunt, J. Chem. Phys. 100, 7875 (1994); ibid, 9276 (1994). Based on our results for Δμ, we find excellent agreement for the binary rototranslational absorption spectrum of H2 at 297.5 K as calculated by X. Li, K. L. C. Hunt, F. Wang, M. Abel, and L. Frommhold, Int. J. Spectroscopy 2010, 371201 (2010) and as determined experimentally by G. Bachet, E. R. Cohen, P. Dore, and G. Birnbaum, Can. J. Phys. 61, 591 (1983), out to ∼1500 cm-1. We have also calculated the vibrational spectra out to 20,000 cm-1, at T = 600 K, 1000 K, and 2000 K, for which there are no experimental data. We are currently working to extend the temperature range in the calculations to 7000 K, for application in modeling the spectra of cool white dwarf stars. We have used the results for Δα to calculate collision-induced rototranslational Raman spectra for H2 pairs [M. Gustafsson, L. Frommhold, X. Li, and K. L. C. Hunt, J. Chem. Phys. 130, 164314 (2009)]. Experimental results for the Raman spectra have been reported by U. Bafile, M. Zoppi, F. Barocchi, M. S. Brown, and L. Frommhold, Phys. Rev. A 40, 1654 (1989); U. Bafile, L. Ulivi, M. Zoppi, F. Barocchi, M. Moraldi, and A. Borysow, Phys. Rev. A 42, 6916 (1990); and M. S. Brown, S.-K. Wang, and L. Frommhold, Phys. Rev. A 40, 2276 (1989). Agreement between our calculations and experiment is good for both the polarized and depolarized spectra, with the remaining discrepancies probably attributable to the difference between the static (calculated) and frequency-dependent (experimental) values of Δα.
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| 8. |
- Li, Xiaoping, et al.
(författare)
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The anisotropic polarizability of pairs of hydrogen molecules and the depolarized collision-induced roto-translational Raman light scattering spectra
- 2010
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Ingår i: Journal of Computational Methods in Sciences and Engineering. - 1472-7978 .- 1875-8983. ; 10:3-6, s. 367-399
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Tidskriftsartikel (refereegranskat)abstract
- In earlier work, Li, Ahuja, Harrison, and Hunt have calculated the collision-induced polarizability Δα of a pair of hydrogen molecules at CCSD(T) level with an aug-cc-pV5Z basis, for 178 relative orientations of the pair, with the bond length in each molecule fixed at r=1.449 a.u. Here we present new results from an expansion of the second-rank tensor components of Δα as series in the spherical harmonics of the molecular orientation angles and the orientation angles of the intermolecular vector. The coefficients in this expansion depend on the separation R between the molecules. We compare the ab initio coefficients with predictions from long-range perturbation theory, including the dipole-induced-dipole interactions at first and second order, higher-multipole induction, effects of nonuniform local fields, hyperpolarization, and van der Waals dispersion. Li and Hunt have derived equations for the long-range coefficients complete to order R^{-6}, using spherical-tensor methods developed by Bancewicz, Głaz, and Kielich for collision-induced light scattering by centrosymmetric linear molecules. We also give new results here for the van der Waals dispersion terms in both isotropic and anisotropic polarizability coefficients. We have calculated these coefficients by 64-point Gauss-Legendre quadrature, using the H_{2} polarizabilities and hyperpolarizabilities at imaginary frequencies computed by Bishop and Pipin, with explicitly correlated wave functions for isolated H_{2} molecules. We show that the ab initio values for the larger anisotropic polarizability coefficients converge to the predictions of the long-range theory, as the separation R between the molecules increases. The coefficients computed ab initio have been used by Gustafsson, Frommhold, Li, and Hunt to calculate the depolarized collision-induced roto-translational Raman spectra of hydrogen gas at 36 K and 50 K out to 800~cm^{-1}, and at 296 K out to 300 cm^{-1}. The general features of the experimental spectra are well reproduced, although the calculated intensities are ∼30% too large over much of the frequency range.
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