| 1. |
- Gustafsson, Magnus, 1969-
(författare)
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Hydrogen dimer features in low temperature collision-induced spectra
- 2017
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Ingår i: Journal of Physics, Conference Series. - : Institute of Physics (IOP). - 1742-6588 .- 1742-6596. ; 810:1
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Tidskriftsartikel (refereegranskat)abstract
- The absorption of radiation in pure hydrogen (H2) gas around the S(0) and S(1) rotational transitions is computed at 20 K and compared with laboratory data. All transitions involving free state are included in the calculations of the absolute absorption. These calculations are done with an isotropic approximation for the H2–H2 pair potential. Agreement with the experiment is observed around the S(0) transition, while the computational approach appears to be slightly worse around the S(1) transition. The positions for bound-to-bound transitions are computed including the full anisotropic pair potential. The anisotropy seems to be crucial to achieve agreement with the measured bound-to-bound transition frequencies. However, those transitions contribute little to the total absorption. The present computed absolute absorptions will provide improved input for radiative transfer models of planetary atmospheres.
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| 2. |
- Zámečníková, Martina, et al.
(författare)
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Formation of CO+ by radiative association II
- 2020
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 492:3, s. 3794-3802
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Tidskriftsartikel (refereegranskat)abstract
- Radiative association of an oxygen atom with a carbon cation is investigated using quantal and semiclassical methods. The total rate coefficient for spontaneous radiative association of O(2s22p4, 3P) with C+(2s22p, 2P) on the doublet manifold is determined from the corresponding cross-sections. The cross-sections for the 12 Σ - → A2 II, 22 Σ - → A2II, and C2 Δ → A2II continuum-bound processes are calculated either semiclassically, in combination with the Breit-Wigner approach, or fully quantum mechanically. In the temperature range 10-10 000 K, our recommended total rate coefficient, obtained from these calculations and the data of Zámecniková et al. (2019), slowly increases from 7.5 × 10-18 cm3s-1 to 2.1 × 10-17 cm3s-1. Corresponding aspects of the CO+ and CO formations in SN 1987A are discussed
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| 3. |
- 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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| 4. |
- Fakhardji, Wissam, et al.
(författare)
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Collision-induced absorption in Ar–Kr gas mixtures : A molecular dynamics study with new potential and dipole data
- 2019
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 151:14
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Tidskriftsartikel (refereegranskat)abstract
- We have implemented a scheme for classical molecular dynamics simulations of collision-induced absorption. The program has been applied to a gas mixture of argon (Ar) and krypton (Kr). The simulations are compared with accurate quantum dynamical calculations. The comparisons of the absorption coefficients show that classical molecular dynamics is correct within 10% for photon wave numbers up to 220 cm−1 at a temperature of 200 K for this system. At higher temperatures, the agreement is even better. Molecular dynamics accounts for many-body interactions, which, for example, give rise to continuous dimer formation and destruction in the gas. In this way, the method has an advantage compared with bimolecular classical (trajectory) treatments. The calculations are carried out with a new empirical Ar–Kr pair potential. This has been obtained through extensive analysis of experimental thermophysical and transport properties. We also present a new high level ab initio Ar–Kr potential curve for comparison, as well as ab initio interaction-induced dipole curves computed with different methods. In addition, the Ar–Kr polarizability and hyperpolarizability are reported. A comparison of the computed absorption spectra with an experiment taken at 300 K shows satisfactory agreement although a difference in absolute magnitude of 10%–15% persists. This discrepancy we attribute mainly to experimental uncertainty.
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| 5. |
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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. |
- Gustafsson, Magnus, 1969-, et al.
(författare)
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Semiclassical methods for calculating radiative association rate constants for different thermodynamic conditions : Application to formation of CO, CN, and SiN
- 2019
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 150:22
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Tidskriftsartikel (refereegranskat)abstract
- It is well-known that resonances can serve as a catalyst for molecule formation. Rate constants for resonance-induced molecule formation are phenomenological as they depend upon the mechanism used to populate the resonances. Standard treatments assume tunneling from the continuum is the only available population mechanism, which means long-lived quasibound states are essentially unpopulated. However, if a fast resonance population mechanism exists, the long-lived quasibound states may be populated and give rise to a substantial increase in the molecule formation rate constant. In the present work, we show that the semiclassical formula of Kramers and ter Haar [Bull. Astron. Inst. Neth. 10, 137 (1946)] may be used to compute rate constants for radiative association in the limit of local thermodynamic equilibrium. Comparisons are made with quantum mechanical and standard semiclassical treatments, and results are shown for two limits which provide upper and lower bounds for the six most important radiative association reactions leading to the formation of CO, CN, and SiN. These results may have implications for interstellar chemistry in molecular clouds, where the environmental and thermodynamic conditions often are uncertain.
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| 8. |
- Gustafsson, Magnus, 1969, et al.
(författare)
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The rate constant for radiative association of HF. Comparing quantum and classical dynamics.
- 2014
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 140:18
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Tidskriftsartikel (refereegranskat)abstract
- Radiative association for the formation of hydrogen fluoride through the A 1Π → X 1Σ+ and X 1Σ+ → X 1Σ+ transitions is studied using quantum and classical dynamics. The total thermal rate constant is obtained for temperatures from 10 K to 20 000 K. Agreement between semiclassical and quantum approaches is observed for the A 1Π → X 1Σ+ rate constant above 2000 K. The agreement is explained by the fact that the corresponding cross section is free of resonances for this system. At temperatures below 2000 K we improve the agreement by implementing a simplified semiclassical expression for the rate constant, which includes a quantum corrected pair distribution. The rate coefficient for the X 1Σ+ → X 1Σ+ transition is calculated using Breit–Wigner theory and a classical formula for the resonance and direct contributions, respectively. In comparison with quantum calculations the classical formula appears to overestimate the direct contribution to the rate constant by about 12% for this transition. Below about 450 K the resonance contribution is larger than the direct, and above that temperature the opposite holds. The biggest contribution from resonances is at the lowest temperature in the study, 10 K, where it is more than four times larger than the direct. Below 1800 K the radiative association rate constant due to X 1Σ+ → X 1Σ+ transitions dominates over A 1Π → X 1Σ+, while above that temperature the situation is the opposite.
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| 9. |
- Karman, Tijs, et al.
(författare)
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Update of the HITRAN collision-induced absorption section
- 2019
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Ingår i: Icarus. - : Elsevier. - 0019-1035 .- 1090-2643. ; 328, s. 160-175
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Tidskriftsartikel (refereegranskat)abstract
- Correct parameterization of the Collision-induced Absorption (CIA) phenomena is essential for accurate modeling of planetary atmospheres. The HITRAN spectroscopic database provides these parameters in a dedicated section. Here, we significantly revise and extend the HITRAN CIA data with respect to the original effort described in Richard et al. [JQSRT 113, 1276 (2012)]. The extension concerns new collisional pairs as well as wider spectral and temperature ranges for the existing pairs. The database now contains CIA for N2N2, N2H2, N2-CH4, N2H2O, N2O2, O2O2, O2-CO2, CO2-CO2, H2H2, H2He, H2-CH4, H2H, HHe, CH4-CH4, CH4-CO2, CH4He, and CH4Ar collision pairs. The sources of data as well as their validation and selection are discussed. A wish list to eliminate remaining deficiencies or lack of data from the astrophysics perspective is also presented.
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| 10. |
- Szabo, Peter, 1988-, et al.
(författare)
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Formation of the NH molecule and its isotopologues through radiative association
- 2019
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press. - 0035-8711 .- 1365-2966. ; 483:3, s. 3574-3578
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Tidskriftsartikel (refereegranskat)abstract
- The rate coefficients and the cross-sections for the formation of imidogen (NH) molecule (and its isotopologues: 15NH and ND) through radiative association are determined by employing quantum mechanical perturbation theory, classical Larmor formula, and Breit–Wigner theory. We suggest the radiative association process as possible route for NH production in diffuse interstellar clouds.
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