scholarly journals Excitation and charge transfer in low-energy hydrogen atom collisions with neutral carbon and nitrogen

2019 ◽  
Vol 625 ◽  
pp. A78 ◽  
Author(s):  
A. M. Amarsi ◽  
P. S. Barklem
Keyword(s):  
Charge Transfer ◽  
Neutral Hydrogen ◽  
Stellar Atmospheres ◽  
Low Energy ◽  
Rate Coefficients ◽  
Collision Dynamics ◽  
Hydrogen Atoms ◽  
Stellar Spectra ◽  
Zero Rate ◽  
Excitation Processes

Low-energy inelastic collisions with neutral hydrogen atoms are important processes in stellar atmospheres, and a persistent source of uncertainty in non-LTE modelling of stellar spectra. We have calculated and studied excitation and charge transfer of C I and of N I due to such collisions. We used a previously presented method that is based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions for the adiabatic potential energies, combined with the multichannel Landau-Zener model for the collision dynamics. We find that charge transfer processes typically lead to much larger rate coefficients than excitation processes do, consistent with studies of other atomic species. Two-electron processes were considered and lead to non-zero rate coefficients that can potentially impact statistical equilibrium calculations. However, they were included in the model in an approximate way, via an estimate for the two-electron coupling that was presented earlier in the literature: the validity of these data should be checked in a future work.

scholarly journals Excitation and charge transfer in low-energy hydrogen atom collisions with neutral oxygen

2018 ◽  
Vol 610 ◽  
pp. A57 ◽  
Author(s):  
P. S. Barklem
Keyword(s):  
Charge Transfer ◽  
Hydrogen Atom ◽  
Electron Transition ◽  
Low Energy ◽  
Rate Coefficients ◽  
Zener Model ◽  
Stellar Spectra ◽  
Excitation Processes ◽  
Covalent Interactions ◽  
Atom System

Excitation and charge transfer in low-energy O+H collisions is studied; it is a problem of importance for modelling stellar spectra and obtaining accurate oxygen abundances in late-type stars including the Sun. The collisions have been studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals (LCAO) model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model. The method has been extended to include configurations involving excited states of hydrogen using an estimate for the two-electron transition coupling, but this extension was found to not lead to any remarkably high rates. Rate coefficients are calculated for temperatures in the range 1000–20 000 K, and charge transfer and (de)excitation processes involving the first excited S-states, 4s.5So and 4s.3So, are found to have the highest rates.

Data on inelastic processes in low-energy collisions of barium atoms and ions with hydrogen atoms and anions

2018 ◽  
Vol 478 (3) ◽  
pp. 3952-3960 ◽  
Author(s):  
Andrey K Belyaev ◽  
Svetlana A Yakovleva
Keyword(s):  
Rate Coefficient ◽  
Molecular State ◽  
Empirical Method ◽  
Stellar Atmospheres ◽  
Low Energy ◽  
Rate Coefficients ◽  
Quantum Model ◽  
Final States ◽  
Hydrogen Atoms ◽  
Excitation Processes

ABSTRACT Inelastic rate coefficients for 686 partial processes in low-energy Ba + H, Ba+ + H−, Ba++ H and Ba2+ + H− collisions are calculated. These data are needed for the non-local thermodynamic equilibrium (non-LTE) modelling of Ba i and Ba ii spectra, especially in cool stellar atmospheres. The calculations of the rate coefficients are performed by means of the quantum model approach, based on the asymptotic semi-empirical method for the electronic structure calculations and on multichannel formulas for the non-adiabatic nuclear dynamical calculations. The inelastic rate coefficients for all transitions between the 17 lowest covalent states and one ionic molecular state in Ba + H and Ba+ + H− collisions, as well as the inelastic rate coefficients for all transitions between the 19 lowest covalent states and one ionic molecular state in Ba+ + H and Ba2+ + H− collisions are calculated. In Ba+ + H− collisions, the highest rate coefficients correspond to the mutual neutralization processes into the   Ba(6s6p1P°), Ba(6s7s3S) and   Ba(6s7s1S) final states, with the largest value of 5.93 × 10−8 cm3 s−1 at T = 6000 K for the process Ba+ + H− →   Ba(6s7s3S) + H. The highest rate coefficient for excitation and de-excitation processes in Ba + H collisions corresponds to the   Ba(6s7s1S) →  Ba(6s7s3S) transition, with the value of 7.62 × 10−9 cm3 s−1 at T = 6000 K. In Ba2+ + H− collisions, the highest rate coefficients correspond to the neutralization processes into the Ba+( 7p2P°), Ba+( 4f 2F°), Ba+( 6d 2D) and Ba+( 7s 2S) final states. The highest neutralization rate has the value of 3.96 × 10−8 cm3 s−1 at T = 6000 K for the Ba2+ + H− → Ba+( 7p 2P°) + H process. The largest rate coefficient for excitation and de-excitation processes in Ba+ + H collisions corresponds to the Ba+(7s 2S) → Ba+( 6p 2P°) transition, with the value of 1.23 × 10−9  cm3 s−1 at T = 6000 K.

scholarly journals Excitation and charge transfer in low-energy hydrogen atom collisions with neutral iron

2018 ◽  
Vol 612 ◽  
pp. A90 ◽  
Author(s):  
P. S. Barklem
Keyword(s):  
Charge Transfer ◽  
Hydrogen Atom ◽  
Low Energy ◽  
Rate Coefficients ◽  
Zener Model ◽  
Atomic Orbitals ◽  
Excitation Processes ◽  
Ionic States ◽  
Covalent Interactions ◽  
Atom System

Data for inelastic processes due to hydrogen atom collisions with iron are needed for accurate modelling of the iron spectrum in late-type stars. Excitation and charge transfer in low-energy Fe+H collisions is studied theoretically using a previously presented method based on an asymptotic two-electron linear combination of atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multi-channel Landau–Zener model. An extensive calculation including 166 covalent states and 25 ionic states is presented and rate coefficients are calculated for temperatures in the range 1000–20 000 K. The largest rates are found for charge transfer processes to and from two clusters of states around 6.3 and 6.6 eV excitation, corresponding in both cases to active 4d and 5p electrons undergoing transfer. Excitation and de-excitation processes among these two sets of states are also significant.

scholarly journals Excitation and charge transfer in low-energy hydrogen atom collisions with neutral manganese and titanium

2020 ◽  
Vol 637 ◽  
pp. A28
Author(s):  
J. Grumer ◽  
P. S. Barklem
Keyword(s):  
Charge Transfer ◽  
Hydrogen Atom ◽  
Low Energy ◽  
Rate Coefficients ◽  
Zener Model ◽  
Excitation Processes ◽  
Ionic States ◽  
Covalent Interactions ◽  
Ionic Limit ◽  
Atom System

Data for inelastic processes due to hydrogen atom collisions with manganese and titanium are needed for accurate modeling of the corresponding spectra in late-type stars. In this work excitation and charge transfer in low-energy Mn+H and Ti+H collisions have been studied theoretically using a method based on an asymptotic two-electron linear combination of an atomic orbitals model of ionic-covalent interactions in the neutral atom-hydrogen-atom system, together with the multichannel Landau-Zener model to treat the dynamics. Extensive calculations of charge transfer (mutual neutralization, ion-pair production), excitation and de-excitation processes in the two collisional systems are carried out for all transitions between covalent states dissociating to energies below the first ionic limit and the dominating ionic states. Rate coefficients are determined for temperatures in the range 1000–20 000 K in steps of 1000 K. Like for earlier studies of other atomic species, charge transfer processes are found to lead to much larger rate coefficients than excitation processes.

Inelastic processes in oxygen–hydrogen collisions

2019 ◽  
Vol 487 (4) ◽  
pp. 5097-5105 ◽  
Author(s):  
A K Belyaev ◽  
Ya V Voronov ◽  
A Mitrushchenkov ◽  
M Guitou ◽  
N Feautrier
Keyword(s):  
Cross Sections ◽  
Short Range ◽  
Calculated Data ◽  
Current Method ◽  
Quantum Probability ◽  
Rate Coefficients ◽  
Stellar Spectra ◽  
Internuclear Distances ◽  
Excitation Processes ◽  
Ionic States

ABSTRACT New accurate theoretical rate coefficients for (de)-excitation and charge transfer in low-energy O + H, O+ + H− and O− + H+ collisions are reported. The calculations of cross-sections and rate coefficients are performed by means of the quantum probability current method, using full configuration interaction ab initio electronic structure calculations that provide a global description of all 43 lowest molecular states from short to asymptotic internuclear distances. Thus, both long- and short-range non-adiabatic regions are taken into account for the first time. All the doublet, quartet and sextet OH molecular states, with excitation energy asymptotes up to 12.07 eV, as well as the two lowest ionic states with the asymptotes O−H+ and O+H− are treated. Calculations are performed for the collision energy range 0.01–100eV and the temperature range 1 000–10 000 K. The mechanisms underlying the processes are analysed: it is shown that the largest rate coefficients, with values exceeding 10−8 cm3 s−1, are due to ionic–covalent interactions present at large internuclear distances, while short-range interactions play an important role for rates with moderate values involved in (de)-excitation processes. As a consequence, a comparison of the present data with previously published results shows that differences of up to several orders of magnitude exist for rate coefficients with moderate values. It is worth pointing out the relatively large rate coefficients for triplet–quintuplet oxygen transitions, as well as for transitions between the O$(\rm 2p^{3}3s\, ^{5}$So) and O$(\rm 2p^{3}3p\, ^{5}$P) levels of the oxygen triplet and H(n = 2) levels. The calculated data are important for modelling stellar spectra, leading to accurate oxygen abundances.

scholarly journals Cobalt-Hydrogen Atomic and Ionic Collisional Data

Atoms ◽  
2020 ◽  
Vol 8 (3) ◽  
pp. 34
Author(s):  
Svetlana A. Yakovleva ◽  
Andrey K. Belyaev ◽  
Maria Bergemann
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Ion Pair ◽  
Pair Formation ◽  
Stellar Atmospheres ◽  
Rate Coefficients ◽  
Line Formation ◽  
Non Local ◽  
Excitation Processes ◽  
Inelastic Processes ◽  
Ionized Systems

Rate coefficients for inelastic processes in low-energy Co + H, Co + + H − , Co + + H , and Co 2 + + H − collisions are estimated using the quantum simplified model. Considerations include 44 triplet and 55 quintet molecular states of CoH, as well as 91 molecular states of CoH + . The estimations provide the rate coefficients for the 4862 partial processes (mutual neutralization, ion-pair formation, excitation, and de-excitation) in the neutral CoH system, and for the 8190 partial processes in the ionized CoH + system, 13 , 052 processes in total. At T = 6000 K, the rate coefficients with the largest values around 6 × 10 − 8 cm 3 s − 1 correspond to the mutual neutralization processes into the Co ( e 2 F ) + H and Co + ( g 5 F ) + H final channels in the neutral and ionized systems, respectively. Among the excitation and de-excitation processes in Co + H and in Co + + H collisions, at T = 6000 K, the largest rate coefficients have values around 7 × 10 − 9 cm 3 s − 1 and correspond to the processes Co ( y 2 S ∘ ) + H → Co ( e 2 F ; v 4 D ∘ ) + H and Co + ( h 3 P ) + H → Co + ( g 3 P ; g 5 P ; g 5 F ) + H , respectively. The calculations single out inelastic processes important for non-local thermodynamic equilibrium (NLTE) modelling of Co I and Co II spectra in stellar atmospheres. The test NLTE calculations are carried out, and it is found that the new collision rates have a strong effect on the line formation and NLTE abundance corrections.

Charge transfer and excitation processes in low energy collisions of He+ ions with Li atoms

2021 ◽  
Vol 21 (8) ◽  
pp. 210
Author(s):  
Xiao-Xia Wang ◽  
Kun Wang ◽  
Yi-Geng Peng ◽  
Chun-Hua Liu ◽  
Ling Liu ◽  
...  
Keyword(s):  
Charge Transfer ◽  
Low Energy ◽  
Excitation Processes

scholarly journals Процессы возбуждения при столкновениях электронов с молекулами глутамина

2020 ◽  
Vol 46 (16) ◽  
pp. 35
Author(s):  
Н.М. Эрдевди ◽  
А.И. Булгакова ◽  
О.Б. Шпеник ◽  
А.Н. Завилопуло
Keyword(s):  
Gas Phase ◽  
Emission Spectra ◽  
Optical Emission ◽  
Low Energy ◽  
Molecular Fragments ◽  
Hydrogen Atoms ◽  
Low Energy Electrons ◽  
Atomic Lines ◽  
Excitation Processes ◽  
Optical Emission Spectra

Excitation processes in collisions of low-energy electrons (1-100 eV) with glutamine molecules in the gas phase have been studied. The optical emission spectra were measured in the wavelength range from 250-520 nm and it was found that, as a result of the decomposition of glutamine molecules, OH molecular emissions and some other molecular fragments are most efficiently formed. And excited hydrogen atoms are also detected. It was found that the excitation thresholds of molecular emissions are 10–12 eV, while the atomic lines of hydrogen are 13–15 eV. The energy dependences of the excitation of individual emissions from a threshold to 50 eV are also presented.

scholarly journals The GALAH Survey: non-LTE departure coefficients for large spectroscopic surveys

2020 ◽  
Vol 642 ◽  
pp. A62
Author(s):  
A. M. Amarsi ◽  
K. Lind ◽  
Y. Osorio ◽  
T. Nordlander ◽  
M. Bergemann ◽  
...  
Keyword(s):  
Local Thermodynamic Equilibrium ◽  
Neutral Hydrogen ◽  
Recent Model ◽  
Stellar Atmospheres ◽  
Inelastic Collisions ◽  
Data Sets ◽  
Simplified Models ◽  
Analysis Pipeline ◽  
Stellar Spectra ◽  
The Galaxy

Massive sets of stellar spectroscopic observations are rapidly becoming available and these can be used to determine the chemical composition and evolution of the Galaxy with unprecedented precision. One of the major challenges in this endeavour involves constructing realistic models of stellar spectra with which to reliably determine stellar abundances. At present, large stellar surveys commonly use simplified models that assume that the stellar atmospheres are approximately in local thermodynamic equilibrium (LTE). To test and ultimately relax this assumption, we have performed non-LTE calculations for 13 different elements (H, Li, C, N, O, Na, Mg, Al, Si, K, Ca, Mn, and Ba), using recent model atoms that have physically-motivated descriptions for the inelastic collisions with neutral hydrogen, across a grid of 3756 1D MARCS model atmospheres that spans 3000 ≤ Teff∕K ≤ 8000, − 0.5 ≤log g∕cm s−2 ≤ 5.5, and − 5 ≤ [Fe/H] ≤ 1. We present the grids of departure coefficients that have been implemented into the GALAH DR3 analysis pipeline in order to complement the extant non-LTE grid for iron. We also present a detailed line-by-line re-analysis of 50 126 stars from GALAH DR3. We found that relaxing LTE can change the abundances by between − 0.7 dex and + 0.2 dex for different lines and stars. Taking departures from LTE into account can reduce the dispersion in the [A/Fe] versus [Fe/H] plane by up to 0.1 dex, and it can remove spurious differences between the dwarfs and giants by up to 0.2 dex. The resulting abundance slopes can thus be qualitatively different in non-LTE, possibly with important implications for the chemical evolution of our Galaxy. The grids of departure coefficients are publicly available and can be implemented into LTE pipelines to make the most of observational data sets from large spectroscopic surveys.

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