| 1. |
- Belyaev, Andrey K., et al.
(författare)
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Ab initio cross sections for low-energy inelastic Mg+H collisions
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:9, s. 092002-
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Tidskriftsartikel (refereegranskat)abstract
- Full quantum scattering calculations of cross sections for low-energy near-threshold inelastic Mg + H collisions are reported, such processes being of interest for modelling of Mg spectral lines in stellar atmospheres. Nonadiabatic transions associated with radial couplings at avoided ionic crossings in the 2Σ+ molecular states are found to be the main mechanism for excitation and ion-pair production processes.
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| 2. |
- Belyaev, Andrey K., et al.
(författare)
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Cross sections for low-energy inelastic Mg + H and Mg+ + H- collisions
- 2012
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 85:3, s. 032704-
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Tidskriftsartikel (refereegranskat)abstract
- We report full quantum scattering calculations for low-energy near-threshold inelastic cross sections in Mg + H and Mg+ + H- collisions. The calculations include all transitions between the eight lowest adiabatic MgH((2)Sigma(+)) molecular states, with the uppermost of those diabatically extended to the ionic molecular state in the asymptotic region. This allows us to treat the excitation processes between the seven lowest atomic states of magnesium in collisions with hydrogen atoms, as well as the ion-pair production and the mutual neutralization processes. The collision energy range is from threshold up to 10 eV. These results are important for astrophysical modeling of spectra in stellar atmospheres. The processes in question are carefully examined and several process mechanisms are found. Some mechanisms are determined by interactions between ionic and covalent configurations at relatively large internuclear distances, while others are based on short-range nonadiabatic regions due to interactions between covalent configurations.
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| 3. |
- Belyaev, Andrey K.
(författare)
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Inelastic aluminium-hydrogen collision data for non-LTE applications in stellar atmospheres
- 2013
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 560, s. A60-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Rate coefficients for inelastic Al + H and Al+ + H- collisions are calculated for all transitions between the seven low-lying levels up to and including the ionic state, namely Al(3p, 4s, 3d, 4p, 5s, nd)+H(1s) and Al+ + H-. The data are needed for non-LTE applications in stellar atmospheres and are presented for a temperature range of 1000-10 000 K.Methods. The calculations were obtained by means of the recently proposed model approach based on the asymptotic method for electronic molecular structure determination and on the branching probability current method for the nonadiabatic nuclear dynamics.Results. It is shown that the processes with the highest rates are the excitation and de-excitation ones between the Al(3d), Al(4p) and Al(4s) states in collisions with H, as well as the ion-pair formation and the mutual neutralization processes between these states and the ionic state.
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| 4. |
- Belyaev, Andrey K., et al.
(författare)
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Inelastic silicon-hydrogen collision data for non-LTE applications in stellar atmospheres
- 2014
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 572, s. A103-
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Tidskriftsartikel (refereegranskat)abstract
- Aims. Inelastic processes in low-energy Si + H and Si+ + H- collisions are treated for the states from the ground state up to the ionic state, in order to provide rate coefficients needed for non-LTE modeling of Si in cool stellar atmospheres. Methods. Electronic molecular structure is determined using a recently proposed model approach based on an asymptotic method in combination with available ab initio potentials. Nonadiabatic nuclear dynamics are treated by means of a combination of multichannel formulas and the branching-probability-current method, based on the Landau-Zener model for nonadiabatic transition probabilities. Results. Cross sections and rate coefficients for inelastic processes in Si + H and Si+ + H- collisions for all transitions between 26 low-lying states plus the ionic state are calculated. It is shown that the highest rate coefficient values correspond to the excitation, de-excitation, ion-pair formation, and mutual neutralization processes involving the Si(3p4p D-3), Si(3p3d F-3), Si(3p4p D-1), Si(3p3d P-3), Si(3p4p S-1), and the ionic Si+ + H- states. These processes are likely to be important in non-LTE modeling.
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| 5. |
- Belyaev, Andrey K., et al.
(författare)
-
Low-energy inelastic Na + H collisions
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:9, s. 092001-
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Tidskriftsartikel (refereegranskat)abstract
- We report full quantum scattering calculations for near-threshold collision cross sections for excitation of Na by H. The calculations include contributions from transitions between all singlet states up to and including the ionic state (ion-pair production). The dynamics calculations are based on three sets of recent ab initio and pseudo-potential quantum-chemical calculations. Considerable sensitivity to the couplings employed is found.
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| 6. |
- Belyaev, Andrey K.
(författare)
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Model approach for low-energy inelastic atomic collisions and application to Al+ H and Al+ + H-
- 2013
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 88:5, s. 052704-
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Tidskriftsartikel (refereegranskat)abstract
- A model approach is derived for estimates of cross sections and rate coefficients in low-energy inelastic collisions of hydrogen atoms and negative ions with other atoms and positive ions, which are of astrophysical interests. The approach is based on the asymptotic method for electronic molecular structure determination and on the branching probability current method for a nonadiabatic nuclear dynamical treatment. The derived approach is applied to low-energy Al + H and Al+ + H- inelastic collisions. It is shown that the processes with the largest values of cross sections and rates are the excitation and de-excitation ones between the Al(3d) and Al(4p) states in collisions with H, as well as the ion-pair formation and the mutual neutralization processes between these states and the ionic state; the second largest cross sections correspond to the similar processes involving the Al(4s) state. The mechanisms of the processes are discussed in detail.
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| 7. |
- Belyaev, Andrey K., et al.
(författare)
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Nonadiabatic nuclear dynamics in the ammonia cation studied by the branching classical trajectory method
- 2012
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Ingår i: Journal of Physics, Conference Series. - : IOP Publishing. - 1742-6588 .- 1742-6596. ; 388:10, s. 102005-
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Tidskriftsartikel (refereegranskat)abstract
- The photoinduced nonadiabatic nuclear dynamics of the ammonia cation is studied by the branching classical trajectory approach. The time-dependent populations of different electronic states of the ammonia cation are calculated and are in good agreement with the results of full quantum calculations.
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| 8. |
- Belyaev, Andrey K., et al.
(författare)
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Nonadiabatic nuclear dynamics of atomic collisions based on branching classical trajectories
- 2011
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Ingår i: Physical Review A. Atomic, Molecular, and Optical Physics. - 1050-2947 .- 1094-1622. ; 84:1, s. 014701-
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Tidskriftsartikel (refereegranskat)abstract
- The branching classical trajectory method for inelastic atomic collision processes is proposed. The approach is based on two features: (i) branching of a classical trajectory in a nonadiabatic region and (ii) the nonadiabatic transition probability formulas particularly adapted for a classical trajectory treatment. In addition to transition probabilities and inelastic cross sections, the proposed approach allows one to calculate incoming and outgoing currents. The method is applied to inelastic Na + H collisions providing the results in reasonable agreement with full quantum calculations.
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| 9. |
- Bergemann, Maria, et al.
(författare)
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Solar oxygen abundance
- 2021
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Ingår i: Monthly notices of the Royal Astronomical Society. - : Oxford University Press (OUP). - 0035-8711 .- 1365-2966. ; 508:2, s. 2236-2253
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Tidskriftsartikel (refereegranskat)abstract
- Motivated by the controversy over the surface metallicity of the Sun, we present a re-analysis of the solar photospheric oxygen (O) abundance. New atomic models of O and Ni are used to perform non-local thermodynamic equilibrium (NLTE) calculations with 1D hydrostatic (MARCS) and 3D hydrodynamical (Stagger and Bifrost) models. The Bifrost 3D MHD simulations are used to quantify the influence of the chromosphere. We compare the 3D NLTE line profiles with new high-resolution, R≈700000≈700000, spatially resolved spectra of the Sun obtained using the IAG FTS instrument. We find that the O I lines at 777 nm yield the abundance of log A(O) = 8.74 ± 0.03 dex, which depends on the choice of the H-impact collisional data and oscillator strengths. The forbidden [O I] line at 630 nm is less model dependent, as it forms nearly in LTE and is only weakly sensitive to convection. However, the oscillator strength for this transition is more uncertain than for the 777 nm lines. Modelled in 3D NLTE with the Ni I blend, the 630 nm line yields an abundance of log A(O) = 8.77 ± 0.05 dex. We compare our results with previous estimates in the literature and draw a conclusion on the most likely value of the solar photospheric O abundance, which we estimate at log A(O) = 8.75 ± 0.03 dex.
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