S. S. Tayal

Breit?Pauli Transition Probabilities and Electron Excitation Collision Strengths for Singly Ionized Sulfur

New improved calculations are reported for transition probabilities and electron impact excitation collision strengths for the astrophysically important lines in S II. The collision strengths have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 70 bound levels of S II covering all possible terms of the ground 3s 23p 3 and singly excited 3s3p 4, 3s 23p 23d, 3s 23p 24s, and 3s 23p 24p configurations. The present calculations are more extensive than previous ones, leading to a total 2415 transitions between fine-structure levels. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all fine-structure transitions at electron temperatures in the range from 5000 to 100,000 K. The present results are compared with a variety of other close-coupling calculations and available experimental data. There is an overall good agreement with the recent 18-state calculations by Ramsbottom, Bell, & Stafford and with the 19-state calculations by Tayal for the most part, but some significant differences are also noted for some transitions.

Electron Excitation Collision Strengths for Singly Ionized Nitrogen

Collision strengths for the astrophysically important lines in N II have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 58 bound levels of N II. The 58 target levels belong to the terms of the ground 2s 22p 2 and singly excited 2s2p 3, 2s 22p3s, 2s 22p3p, 2s 22p3d, 2s 22p4s, 2s 22p4p, and 2s2p 23s configurations. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all 1653 fine-structure transitions among the 58 levels at electron temperatures in the range from 500 to 100,000 K. The line strengths, oscillator strengths, and transition probabilities for all E1 transitions are tabulated. The present results are compared with a variety of other close-coupling calculations. There is an overall good agreement with the 23-state calculation by Hudson & Bell in most part, but some significant differences are also noted for some transitions.

Oscillator Strengths and Electron Collision Rates for Fine-Structure Transitions in O II

Electron impact excitation collision strengths for the fine-structure transitions between the lowest 13 levels of the 2s22p3, 2s2p4, and 2s22p23s configurations and from these levels to the next 22 other lowest levels of the 2s2p4, 2s22p23s, and 2s22p23p configurations have been calculated using a 62-level Breit-Pauli R-matrix approach with orthogonal radial functions and a 47-level Breit-Pauli R-matrix approach with nonorthogonal radial functions. A B-spline basis has been used for the description of continuum functions, and no orthogonality constraint has been imposed between the continuum functions and the valence atomic orbitals in 47-level calculation. Oscillator strengths and transition probabilities for the fine-structure transitions have been calculated using nonorthogonal orbitals in the multiconfiguration Hartree-Fock approach. The present oscillator strengths normally compare very well with a previously available calculation. The collision strength is averaged over a Maxwellian velocity distribution to obtain the effective collision strengths as a function of electron temperature. The effective collision strengths are presented over a wide temperature range (2 × 103 to 105 K) suitable for modeling of astrophysical plasmas.

ELECTRON COLLISIONAL EXCITATION RATES FOR O I USING THE B-SPLINE R-MATRIX APPROACH

The B-spline R-matrix approach has been used to calculate electron collisional excitation strengths and rates for transitions between the 3P, 1D, and 1S states of ground configuration and from these states to the states of the excited 2s22p3ns (n = 3-5), 2s22p3np (n = 3-4), 2s22p3nd (n = 3-4), 2s22p34f, and 2s2p5 configurations. The nonorthogonal orbitals are used for an accurate description of both the target wave functions and the R-matrix basis functions. The thermally averaged collision strengths are obtained from the collision strengths by integrating over a Maxwellian velocity distribution of electron energies, and these are tabulated over a temperature range from 1000 to 60,000 K. The parametric functions of scaled energy have also been obtained to represent collision strengths over a wide energy range or thermally averaged collision strengths at any desired temperature.

Breit-Pauli R-Matrix Calculation for Electron Collision Rates in O IV

Electron collision excitation strengths and rates for infrared and ultraviolet lines arising from transitions between the fine-structure levels of the 2s22p, 2s2p2, 2p3, 2s23s, 2s23p, 2s23d, 2s2p3s, 2s2p3p, 2s2p3d, 2s24s, and 2s24p configurations of O IV have been calculated using Breit-Pauli R-matrix approach. Configuration-interaction wave functions have been used for an accurate representation of target levels. These wave functions give excitation energies that are in close agreement with experiment. Oscillator strengths and transition probabilities for UV and EUV lines compare very well with previous calculations. The Rydberg series of resonances converging to the excited levels are explicitly included in the scattering calculation and are found to make substantial contribution to collision strengths. The effective collision strengths are obtained by integrating total collision strengths over a Maxwellian distribution of electron energies, and these are presented over a wide temperature range suitable for modeling of astrophysical plasmas. Significant qualitative and quantitative differences with earlier results of effective collision strengths are noted.

New Accurate Oscillator Strengths and Electron Excitation Collision Strengths for N I

The nonorthogonal orbitals technique in a multiconfiguration Hartree-Fock approach is used to calculate oscillator strengths and transition probabilities of N I lines. The relativistic effects are allowed by means of Breit-Pauli operators. The length and velocity forms of oscillator strengths show good agreement for most transitions. The B-spline R-matrix with pseudostates approach has been used to calculate electron excitation collision strengths and rates. The nonorthogonal orbitals are used for an accurate description of both target wave functions and the R-matrix basis functions. The 24 spectroscopic bound and autoionizing states together with 15 pseudostates are included in the close-coupling expansion. The collision strengths for transitions between fine-structure levels are calculated by transforming the LS-coupled K-matrices to K-matrices in an intermediate coupling scheme. Thermally averaged collision strengths have been determined by integrating collision strengths over a Maxwellian distribution of electron energies over a temperature range suitable for the modeling of astrophysical plasmas. The oscillator strengths and thermally averaged collision strengths are presented for transitions between the fine-structure levels of the 2s22p3 4So, 2Do, 2Po, 2s2p4 4P, 2s22p23s 4P, and 2P terms and from these levels to the levels of the 2s22p23p 2So, 4Do, 4Po, 4So, 2Do, 2Po, 2s22p23s 2D, 2s22p24s 4P, 2P, 2s22p23d 2P, 4F, 2F, 4P, 4D, and 2D terms. Thermally averaged collision strengths are tabulated over a temperature range from 500 to 50,000 K.

Collision Strengths for Electron Collisional Excitation of S II

Electron collisional excitation strengths for inelastic transitions in S II are calculated using the R-matrix method in a 19-state (3s23p34So,2Do,2Po, 3s3p44P,2D,2S, 3s23p23d2P,4F,4D,2F,4P, 3s23p24s4P,2P, 3s23p24p2So,4Do,4Po,2Do,4So,2Po) close-coupling approximation. These target states are represented by extensive configuration-interaction wave functions that give excitation energies and oscillator strengths that are usually in good agreement with the experimental values and the available accurate calculations. The present results for collision strengths are in very good agreement with the recent merged beams energy loss measurement of Liao et al. and agree reasonably well with the 18-state R-matrix calculation of Ramsbottom, Bell, & Stafford, but show significant differences from the 12-state R-matrix calculation of Cai & Pradhan.

Electron Impact Excitation of Fine-Structure Levels in Sulfur-like Fe XI

Collision strengths for electron impact excitation of fine-structure levels in sulfur-like Fe XI are calculated in a semirelativistic R-matrix approach. The 38 fine-structure levels arising from the 20 LS states 3s23p43P,1D,1S; 3s3p53Po,1Po; 3s23p3(4So)3d3Do, 3s23p3(2Po)3d1,3Po,1,3Do,1,3Fo, 3s23p3(2Do)3d1,3So,1,3Po,1,3Do,1,3Fo are included in our calculation. The target levels are represented by configuration interaction wave functions. The relativistic effects are considered in the Breit-Pauli approximation by including one-body mass correction, Darwin term, and spin-orbit terms in the scattering equations. Collision strengths for transitions from the 3s23p43P2,1,0 levels to the fine-structure levels of the 3s23p33d configuration are compared with the distorted-wave results of Bhatia & Doschek at 8.0, 16.0, 24.0 ryd. There are some significant discrepancies between the two calculations, mostly caused by the difference in target wave functions. The collision strengths are integrated over a Maxwellian distribution of electron energies to obtain effective collision strengths over the temperature range from 5 × 105 to 5 × 106 K.

Transition Probabilities and Electron Excitation Rates for Fe XIV

Electron impact excitation rates and oscillator strengths for transitions between fine-structure levels of the 3s23p, 3s3p2, and 3s23d configurations and from these levels to the fine-structure levels of the 3p3, 3s3p3d, and 3p23d configurations in Fe XIV are reported. The 135 target levels have been included in the close-coupling expansion in our collision calculation using the Breit-Pauli R-matrix approach. The lowest 135 Fe XIV energy levels belong to the 3s23p, 3s3p2, 3s23d, 3p3, 3s3p3d, 3p23d, 3s3d2, 3p3d2, 3s24s, 3s24p, 3s3p4s, and 3s24d configurations. An accurate representation of target levels has been obtained using spectroscopic and correlation radial functions. The atomic wave functions give excitation energies which are in close agreement with experiment. Oscillator strengths and transition probabilities for Fe XIV lines normally compare very well with previous calculations. The effective collision strengths have been calculated by integrating total resonant and nonresonant collision strengths over a Maxwellian distribution of electron energies and these are presented over a wide temperature range suitable for modeling of astrophysical plasmas. Significant differences in collision strengths are noted with the previous 18 state R-matrix calculation.

Oscillator Strengths of Allowed and Intercombination Lines in P II

Accurate oscillator strengths and transition probabilities for allowed and intercombination lines of the 3s23p2-3s3p3, 3s23p2-3s23p3d, 3s23p2-3s23p4s, 3s23p2-3s23p5s, 3s23p2-3s23p4d, 3s3p3-3s23p4p, and 3s23p4s-3s23p4p multiplets in P II are calculated by using nonorthogonal orbitals technique in the multiconfiguration Hartree-Fock method. The relativistic corrections are included through the Breit-Pauli Hamiltonian. The wave functions exhibit large correlation corrections and term dependence of valence orbitals. Progressively larger calculations are performed to check for significant electron correlation contributions. The length and velocity forms of oscillator strength show good agreement for most transitions in our final calculation. The calculated branching ratio for the 5S-3P2,1 intercombination lines is in agreement with the experiment and other elaborate calculations.