scholarly journals Inelastic O+H collisions and the O I 777 nm solar centre-to-limb variation

2018 ◽  
Vol 616 ◽  
pp. A89 ◽  
Author(s):  
A. M. Amarsi ◽  
P. S. Barklem ◽  
M. Asplund ◽  
R. Collet ◽  
O. Zatsarinny
Keyword(s):  
Impulse Approximation ◽  
Rate Coefficients ◽  
Line Formation ◽  
Linear Combinations ◽  
Electron Model ◽  
Atomic Orbitals ◽  
Model Based ◽  
Free Electron Model ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

The O I 777 nm triplet is a key diagnostic of oxygen abundances in the atmospheres of FGK-type stars; however, it is sensitive to departures from local thermodynamic equilibrium (LTE). The accuracy of non-LTE line formation calculations has hitherto been limited by errors in the inelastic O+H collisional rate coefficients; several recent studies have used the Drawin recipe, albeit with a correction factor SH that is calibrated to the solar centre-to-limb variation of the triplet. We present a new model oxygen atom that incorporates inelastic O+H collisional rate coefficients using an asymptotic two-electron model based on linear combinations of atomic orbitals, combined with a free electron model based on the impulse approximation. Using a 3D hydrodynamic STAGGER model solar atmosphere and 3D non-LTE line formation calculations, we demonstrate that this physically motivated approach is able to reproduce the solar centre-to-limb variation of the triplet to 0.02 dex, without any calibration of the inelastic collisional rate coefficients or other free parameters. We infer log ϵO = 8.69 ± 0.03 from the triplet alone, strengthening the case for a low solar oxygen abundance.

Calculations of fine-structure resolved collisional rate coefficients for the NH(X3Σ−)-He system

2011 ◽  
Vol 134 (2) ◽  
pp. 024305 ◽  
Author(s):  
Robert Toboła ◽  
Fabien Dumouchel ◽  
Jacek Kłos ◽  
François Lique
Keyword(s):  
Fine Structure ◽  
Rate Coefficients ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

Collisional-Rate Coefficients for Sodiumlike Ar viii Ions

1972 ◽  
Vol 6 (1) ◽  
pp. 38-44 ◽  
Author(s):  
R. U. Datla ◽  
H. -J. Kunze ◽  
D. Petrini
Keyword(s):  
Rate Coefficients ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

Collisional excitation of H2S by molecular hydrogen

2020 ◽  
Vol 494 (4) ◽  
pp. 5239-5243
Author(s):  
Paul J Dagdigian
Keyword(s):  
Energy Surface ◽  
Rate Coefficients ◽  
Cluster Method ◽  
Quantum Scattering ◽  
Collisional Excitation ◽  
Close Coupling ◽  
Accurate Knowledge ◽  
Explicitly Correlated ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

ABSTRACT Accurate estimates of the abundance of H2S, and inferences about the unmeasured H2 density, require accurate knowledge of radiative and collisional rate coefficients. Time-independent close-coupling quantum scattering calculations have been employed to compute rate coefficients for (de-)excitation of para- and ortho-H2S in collisions with para- and ortho-H2. These calculations utilized a potential energy surface for the interaction of H2S with H2 recently computed by the explicitly correlated CCSD(T)-F12a coupled-cluster method. Rate coefficients for temperatures ranging from 5 to 500 K were calculated for all transitions among the first 19 rotational levels of H2S, whose energies are less than or equal to 405 K. These rate coefficients are compared with previous estimates of these quantities.

Rotational (de)-excitation of C5 by collision with He at low temperature

2021 ◽  
Author(s):  
A. Chefai ◽  
M. Ben Khalifa ◽  
F. Khadri ◽  
K. Hammami
Keyword(s):  
Low Temperature ◽  
Interstellar Medium ◽  
Rate Coefficients ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

An appropriate estimation of the abundance of the observed C5 radical in the interstellar medium requires accurate radiative and collisional rate coefficients.

scholarly journals Measurements of Collisional Rate Coefficients in Laboratory Plasmas

1972 ◽  
Vol 14 ◽  
pp. 565-583 ◽  
Author(s):  
H.-J. Kunze
Keyword(s):  
Theoretical Calculations ◽  
Experimental Results ◽  
Experimental Techniques ◽  
Rate Coefficients ◽  
Line Radiation ◽  
Laboratory Plasmas ◽  
Plasma Device ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

AbstractLine radiation emitted by highly ionized atoms embedded in hot laboratory plasmas can be utilized to obtain collisional rate coefficients for excitation and ionization. After a discussion of the principles underlying these measurements, the plasma device mostly used is explained briefly as are the various experimental techniques. All experimental results obtained so far are finally discussed and compared with theoretical calculations where possible.

scholarly journals The excitation of OH by H2 revisited – II. Hyperfine resolved rate coefficients

2020 ◽  
Vol 493 (3) ◽  
pp. 3491-3495 ◽  
Author(s):  
J Kłos ◽  
P J Dagdigian ◽  
M H Alexander ◽  
A Faure ◽  
F Lique
Keyword(s):  
Molecular Clouds ◽  
Emission Spectra ◽  
Rate Coefficients ◽  
Star Forming ◽  
Physical Conditions ◽  
Star Forming Regions ◽  
Wide Range ◽  
State Rate ◽  
Collisional Rate Coefficients ◽  
Collisional Rate

ABSTRACT Observations of hyperfine resolved transitions of the hydroxyl radical (OH) are unique probes of the physical conditions in molecular clouds. In particular, hyperfine intensities can be used as an effective thermometer over a wide range of molecular densities. Accurate modelling of the OH emission spectra requires the calculation of collisional rate coefficients for the excitation of OH by H2, the most abundant collisional partner in the molecular clouds. Here, we determine hyperfine resolved rate coefficients for the excitation of OH by H2 using a recently developed highly accurate potential energy surface. State-to-state rate coefficients between the lower hyperfine levels were calculated using recoupling techniques for temperature ranging from 10 to 150 K. Significant differences were found with the earlier values currently used in astrophysical models, the new rate coefficients being larger than the previous ones. Finally, we compute the excitation of the OH radical in cold molecular clouds and star-forming regions. The new rate coefficients were found to increase the hyperfine intensities by a factor of ∼1–2. Consequently, we recommend using this new set of data in any astrophysical model of OH excitation.

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