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

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.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201732365 ◽

2018 ◽

Vol 612 ◽

pp. A90 ◽

Cited By ~ 15

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.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201731968 ◽

2018 ◽

Vol 610 ◽

pp. A57 ◽

Cited By ~ 13

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.

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

Astronomy and Astrophysics ◽

10.1051/0004-6361/201937434 ◽

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.

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Colloidal CdSe nanocrystals are inherently defective

Nature Communications ◽

10.1038/s41467-021-21153-z ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Tamar Goldzak ◽

Alexandra R. McIsaac ◽

Troy Van Voorhis

Keyword(s):

Charge Transfer ◽

Energy Spectrum ◽

Surface Structure ◽

Short Range ◽

Surface Defects ◽

Low Energy ◽

Lewis Base ◽

Cdse Nanocrystals ◽

Photoinduced Charge Transfer ◽

Photoinduced Charge

AbstractColloidal CdSe nanocrystals (NCs) have shown promise in applications ranging from LED displays to medical imaging. Their unique photophysics depend sensitively on the presence or absence of surface defects. Using simulations, we show that CdSe NCs are inherently defective; even for stoichiometric NCs with perfect ligand passivation and no vacancies or defects, we still observe that the low energy spectrum is dominated by dark, surface-associated excitations, which are more numerous in larger NCs. Surface structure analysis shows that the majority of these states involve holes that are localized on two-coordinate Se atoms. As chalcogenide atoms are not passivated by any Lewis base ligand, varying the ligand should not dramatically change the number of dark states, which we confirm by simulating three passivation schemes. Our results have significant implications for understanding CdSe NC photophysics, and suggest that photochemistry and short-range photoinduced charge transfer should be much more facile than previously anticipated.

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