Low-energy electron collisions with atomic oxygen:<i>R</i>-matrix calculation with non-orthogonal orbitals

Zatsarinny, Oleg; Tayal, S. S.

doi:10.1088/0953-4075/34/7/312

Cited by 46 publications

(77 citation statements)

References 33 publications

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“…However, the different sets of orthogonal orbitals thus obtained for different states are not orthogonal to each other. The nonorthogonal orbitals provide much greater flexibility in the choice of wave functions than the orthogonal orbitals and also allow to include correlation with a reasonable number of configurations and correlated orbitals (Zatsarinny & Tayal 2001). Our calculations are performed using the multi-configuration Hartree-Fock (MCHF) method (Froese Fischer 1991;Zatsarinny & Froese Fischer 2000).…”

Section: Excitation Energies Oscillator Strengths and Lifetimesmentioning

confidence: 99%

“…We used B-spline basis for the description of continuum functions and did not impose any orthogonality constraint between continuum functions and the valence spectroscopic and correlated atomic orbitals (Zatsarinny & Tayal 2001;Zatsarinny 2006). This allowed us to avoid potential inconsistencies between the continuum and bound parts of the close-coupling expansion.…”

Section: Collision Calculationmentioning

confidence: 99%

“…Our scattering calculations are performed by using highly accurate target wave functions and by including fine-structure effects in the close-coupling expansions directly to make sure that the relativistic effects are adequately accounted in the scattering calculation. The present calculations were carried out with the B-spline Breit-Pauli R-matrix (BSR) approach (Zatsarinny & Tayal 2001;Zatsarinny 2006). One of the distinct features of the present method is the use of termdependent non-orthogonal orbital sets in the description of the target states.…”

Section: Introductionmentioning

confidence: 99%

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Breit-Pauli oscillator strengths and electron excitation collision strengths for Si VIII

Tayal

2012

A&A

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Aims. Oscillator strengths and electron impact excitation collision strengths for transitions between the 68 fine-structure levels of the 2s 2 2p 3 , 2s2p 4 , 2p 5 , 2s 2 2p 2 3s, 2s 2 2p 2 3p, 2s 2 2p 2 3d and 2s2p 3 3s configurations in Si VIII are calculated. Thermally averaged collision strengths are presented as a function of electron temperature for application to solar and other astrophysical plasmas. Methods. The collision strengths have been calculated using the B-spline Breit-Pauli R-matrix method for allowed and forbidden transitions in Si VIII. The relativistic effects have been incorporated through mass, Darwin and spin-orbit one-body operators in the Breit-Pauli Hamiltonian in the scattering calculation, while in the calculation of oscillator strengths the one-body and two-body relativistic operators are included. Flexible non-orthogonal sets of spectroscopic and correlation radial functions are used to obtain accurate description of Si VIII levels and to represent the scattering functions. The 68 fine-structure levels of the 2s 2 2p 3 , 2s2p 4 , 2p 5 , 2s 2 2p 2 3s, 2s 2 2p 2 3p, 2s 2 2p 2 3d and 2s2p 3 3s configurations have been considered in both the radiative and scattering calculations. The present scattering calculations are more extensive than previous ones, leading to a total 2278 transitions between fine-structure levels. Results. The calculated excitation energies are in excellent agreement with experiment and represent an improvement over the previous calculations. The present collision strengths show reasonable agreement with the previously available R-matrix and distorted-wave calculations. The oscillator strengths for E1 transitions normally compare very well with previous calculations. The effective collision strengths are obtained by integrating total resonant and non-resonant collision strengths over a Maxwellian distribution of electron energies and these are presented over a wide temperature range from 10 4 to 4.0 × 10 6 K.

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Section: Excitation Energies Oscillator Strengths and Lifetimesmentioning

confidence: 99%

Section: Collision Calculationmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Breit-Pauli oscillator strengths and electron excitation collision strengths for Si VIII

Tayal

2012

A&A

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“…Computer memory limitations often lead to the use of inconsistent sets of N-electron and (N + 1)-electron configurations. We note the existence of methods that may allow this problem to be avoided or its effects drastically reduced, in particular the method developed by Gorczyca et al (1995) and the B-spline R-matrix approach with non-orthogonal orbitals (e.g., Zatsarinny & Froese Fischer 2000;Zatsarinny & Tayal 2001), a code for which was recently published by Zatsarinny (2006). With this in mind, we chose consistent N-and (N + 1)-electron configurations for our calculations.…”

Section: Calculationsmentioning

confidence: 99%

Electron-impact excitation of neutral oxygen

Barklem¹

2006

A&A

105

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Aims. Our goal was to calculate transition rates from ground and excited states in neutral oxygen atoms due to electron collisions for non-LTE modelling of oxygen in late-type stellar atmospheres, thus enabling the reliable interpretation of oxygen lines in stellar spectra. Methods. A 38-state R-matrix calculation in LS -coupling has been performed. Basis orbitals from the literature are adopted, and a large set of configurations are included to obtain good representations of the target wave functions. Rate coefficients are calculated by averaging over a Maxwellian velocity distribution. Results. Estimates for the cross sections and rate coefficients are presented for transitions between the seven lowest LS states of neutral oxygen. The cross sections for excitation from the ground state compare well with existing experimental and recent theoretical results.

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“…Our scattering calculations were performed by using highly accurate target wave functions and by including fine-structure effects in the close-coupling expansions directly to make sure that the relativistic effects are adequately accounted for in the scattering calculations. The present calculations were carried out with the B-spline Breit-Pauli R-matrix (BSR) approach (Zatsarinny & Tayal 2001;Zatsarinny 2006). One of the distinct features of the present method is the use of term-dependent, non-orthogonal orbital sets in the description of the target states.…”

Section: Introductionmentioning

confidence: 99%

Oscillator strengths and effective collision strengths for electron excitation of Mg VI

Tayal

2012

A&A

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Aims. Electron impact excitation collision strengths and oscillator strengths for the astrophysically important lines in Mg VI are reported. Thermally averaged collision strengths are presented as a function of electron temperature for application to solar and other astrophysical plasmas. Methods. The collision strengths were calculated in a close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent, non-orthogonal orbitals was employed for an accurate representation of the target wave functions. The close-coupling expansion includes 74 bound levels of Mg VI covering the n = 2 and n = 3 terms. The present calculations led to a total of 2701 forbidden, intercombination, and allowed transitions between fine-structure levels. The effective collision strengths were obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities.Results. The accuracy of present oscillator strengths is evaluated by the agreement between the length and velocity formulations combined with the agreement between the calculated and measured excitation energies. The calculated excitation energies are in excellent agreement with experiments and other extensive configuration-interaction calculations. The oscillator strengths for all E1 transitions are listed. The effective collision strengths are tabulated for all 2701 transitions among the 74 fine-structure levels at 11 electron temperatures in the range from 10 000 to 200 000 K. The present results are compared with other close-coupling and distorted-wave calculations. Overall good agrement is generally found with the calculations by Ramsbottom & Bell and by Landi & Bhatia for many transitions, but significant differences are also noted for some transitions.

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Low-energy electron collisions with atomic oxygen:R-matrix calculation with non-orthogonal orbitals

Cited by 46 publications

References 33 publications

Breit-Pauli oscillator strengths and electron excitation collision strengths for Si VIII

Breit-Pauli oscillator strengths and electron excitation collision strengths for Si VIII

Electron-impact excitation of neutral oxygen

Oscillator strengths and effective collision strengths for electron excitation of Mg VI

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