Swaraj Tayal | Clark Atlanta University (original) (raw)
Papers by Swaraj Tayal
Bulletin of the American Physical Society, 2010
We present Maxwellian-averaged effective collision strengths for the electron-impact excitation o... more We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S iii over a wide range of electron temperatures of astrophysical importance, log T e (K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations 3s 2 3p 2 , 3s3p 3 , 3s 2 3p3d, 3s 2 3p4s, 3s 2 3p4p and 3s 2 3p4d, giving rise to 1378 individual lines, and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code cloudy to generate line intensities for a range of plasma parameters, with emphasis on allowed UV and EUV emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by FUSE and EUVE. The present line intensities are found to agree well with the observational results and provide a noticeable improvement upon the values predicted by CHIANTI.
Bulletin of the American Physical Society, 2011
ABSTRACT
We have made preliminary calculation for the excitation of oxygen atom from the ground 2p^4 (^3P)... more We have made preliminary calculation for the excitation of oxygen atom from the ground 2p^4 (^3P) to the mtastable 2p^33s (^5S) state. We have used the recently extended MCHF method for multi-open channels to calculate the excitation cross sections. The important electron correlation and polarization effects have been taken into account completely ab-initio by the extended MCHF method. We have also used the R-matrix method to calculate the same to compare with the MCHF results. We will present the comparison of both MCHF and R-matrix results with the available experimental and other theoretical calculations. These results will be useful for astrophysical applications.
Experimental and theoretical collisional excitation cross sections are reported for the transitio... more Experimental and theoretical collisional excitation cross sections are reported for the transitions 3s(sup 2)3p(sup 3) (sup 4)s(deg) (leads to)3s(sup 2)3p(sup 3)(sup 2)D(deg), (sup 2)p(deg) and 3s3p(sup 4) (sup 4)p in s//.
Measurements have been made of the electron excitation cross section for highly-charged positive ... more Measurements have been made of the electron excitation cross section for highly-charged positive ions (HCIs). These ions and charge states are important in interpreting data obtained from the HST, EUVE, FUSE, Chandra and Newton missions. Experimental cross sections are ...
Bulletin of the American Physical Society, 2018
Physical Review A, 2003
Experimental and theoretical electron-excitation cross sections are reported for the 2s 2 2p 2 P ... more Experimental and theoretical electron-excitation cross sections are reported for the 2s 2 2p 2 P o →2s2p 2 4 P and →2s2p 2 2 D transitions in D 3 + . The transition energies are centered at 8.85 and 15.7 eV, respectively. Measurements are made using the energy-loss merged-beams method. The center-of-mass energy range covered is 6.1 (below threshold) to 19.3 eV. Comparison is made with results of new calculations in a 25-state R-matrix theory and with results in a previous eight-state R-matrix calculation. The presence of rich resonance structure is confirmed in both experiment and theory. In most cases there is good agreement in the magnitude of cross section, and energy location of the resonances.
Bulletin of the American Physical Society, 2018
Bulletin of the American Physical Society, 2014
We present Maxwellian-averaged effective collision strengths for the electron-impact excitation o... more We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S iii over a wide range of electron temperatures of astrophysical importance, log T e (K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations 3s 2 3p 2 , 3s3p 3 , 3s 2 3p3d, 3s 2 3p4s, 3s 2 3p4p and 3s 2 3p4d, giving rise to 1378 individual lines, and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code cloudy to generate line intensities for a range of plasma parameters, with emphasis on allowed UV and EUV emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by FUSE and EUVE. The present line intensities are found to agree well with the observational results and provide a noticeable improvement upon the values predicted by CHIANTI.
Bulletin of the American Physical Society, 2016
We present a comprehensive study of electron collisions with boron atoms by using the B-spline R-... more We present a comprehensive study of electron collisions with boron atoms by using the B-spline R-matrix method for electron energies ranging from threshold to 100 eV. Elastic, excitation, and ionization cross sections were obtained for all transitions between the lowest 11 states of boron. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was employed to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo target states of boron were used to check the sensitivity of the results to changes in the theoretical model. The cross-section dataset obtained from the large-scale calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving neutral boron.
Bulletin of the American Physical Society, 2008
Bulletin of the American Physical Society, 2009
Experimental and theoretical collisional excitation cross sections are reported for the transitio... more Experimental and theoretical collisional excitation cross sections are reported for the transitions 3s(exp 2)3p(exp 3)4S(exp o) approaches 3s(exp 2)3p(exp 3) 2D(exp o), 2P(exp o), and 3s3P(exp 4) 4P in S II. The transition wavelengths (energies) are 6716 A (1.85 eV), 4069 A (3.05 eV), and 1256 A (9.87 eV), respectively. In the experiments, use is made of the energy-loss merged-beams method. The metastable fraction of the S II beam was assessed and minimized. The contribution of elastically scattered electrons was reduced by the use of a lowered solenoidal magnetic field and a modulated radio-frequency voltage on the analyzing plates and by retarding grids to reject the elastically scattered electrons with larger Larmor radii. For each transition, comparisons are made among experiments, the new 19 state R-matrix calculation, and three other close-coupling calculations.
The Astrophysical Journal, 2011
New extensive calculations are reported for electron collision strengths, rate coefficients, and ... more New extensive calculations are reported for electron collision strengths, rate coefficients, and transition probabilities for the astrophysically important lines of Fe VIII. 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 102 fine-structure levels of Fe VIII covering all possible terms of the ground 3p 63d and singly excited 3p 53d 2, 3p 64l, 3p 53d4s, 3s3p 63d 2, and 3p 65l configurations. The present calculations are more extensive than the previous ones, leading to a total 5151 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 tran...
Collision strengths for transitions between the 3s23p4 P2, 1, 03, 1D2, and 1S0 levels and from th... more Collision strengths for transitions between the 3s23p4 P2, 1, 03, 1D2, and 1S0 levels and from these levels to the 3s3p5 P02, 1, 03 and 1P01 levels of Fe XI are calculated using a semirelativistic R-matrix approach. The 38 fine-structure levels arising from the 20 LS 3s23p4 P3, 1D, 1S, 3s3p5 P03, 1P0, 3s23p3(4S0)3d D03, 3s23p3(2P0)3d P01,3, 1, 3D0, 1, 3F0, 3s23p3(2D0)3d S01,3, 1, 3P0, 1, 3D0, 1, 3F0 states are included in our calculation. These 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. Complicated resonance structures are found to enhance the collision strengths significantly for many transitions in the threshold energy regions. Our collision strengths are compared with the available results of Bhatia & Doschek at 8.0, 16.0, and 24.0 ryd. The collision strengths are integrated o...
Bulletin of the American Physical Society, 2010
We present Maxwellian-averaged effective collision strengths for the electron-impact excitation o... more We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S iii over a wide range of electron temperatures of astrophysical importance, log T e (K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations 3s 2 3p 2 , 3s3p 3 , 3s 2 3p3d, 3s 2 3p4s, 3s 2 3p4p and 3s 2 3p4d, giving rise to 1378 individual lines, and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code cloudy to generate line intensities for a range of plasma parameters, with emphasis on allowed UV and EUV emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by FUSE and EUVE. The present line intensities are found to agree well with the observational results and provide a noticeable improvement upon the values predicted by CHIANTI.
Bulletin of the American Physical Society, 2011
ABSTRACT
We have made preliminary calculation for the excitation of oxygen atom from the ground 2p^4 (^3P)... more We have made preliminary calculation for the excitation of oxygen atom from the ground 2p^4 (^3P) to the mtastable 2p^33s (^5S) state. We have used the recently extended MCHF method for multi-open channels to calculate the excitation cross sections. The important electron correlation and polarization effects have been taken into account completely ab-initio by the extended MCHF method. We have also used the R-matrix method to calculate the same to compare with the MCHF results. We will present the comparison of both MCHF and R-matrix results with the available experimental and other theoretical calculations. These results will be useful for astrophysical applications.
Experimental and theoretical collisional excitation cross sections are reported for the transitio... more Experimental and theoretical collisional excitation cross sections are reported for the transitions 3s(sup 2)3p(sup 3) (sup 4)s(deg) (leads to)3s(sup 2)3p(sup 3)(sup 2)D(deg), (sup 2)p(deg) and 3s3p(sup 4) (sup 4)p in s//.
Measurements have been made of the electron excitation cross section for highly-charged positive ... more Measurements have been made of the electron excitation cross section for highly-charged positive ions (HCIs). These ions and charge states are important in interpreting data obtained from the HST, EUVE, FUSE, Chandra and Newton missions. Experimental cross sections are ...
Bulletin of the American Physical Society, 2018
Physical Review A, 2003
Experimental and theoretical electron-excitation cross sections are reported for the 2s 2 2p 2 P ... more Experimental and theoretical electron-excitation cross sections are reported for the 2s 2 2p 2 P o →2s2p 2 4 P and →2s2p 2 2 D transitions in D 3 + . The transition energies are centered at 8.85 and 15.7 eV, respectively. Measurements are made using the energy-loss merged-beams method. The center-of-mass energy range covered is 6.1 (below threshold) to 19.3 eV. Comparison is made with results of new calculations in a 25-state R-matrix theory and with results in a previous eight-state R-matrix calculation. The presence of rich resonance structure is confirmed in both experiment and theory. In most cases there is good agreement in the magnitude of cross section, and energy location of the resonances.
Bulletin of the American Physical Society, 2018
Bulletin of the American Physical Society, 2014
We present Maxwellian-averaged effective collision strengths for the electron-impact excitation o... more We present Maxwellian-averaged effective collision strengths for the electron-impact excitation of S iii over a wide range of electron temperatures of astrophysical importance, log T e (K) = 3.0-6.0. The calculation incorporates 53 fine-structure levels arising from the six configurations 3s 2 3p 2 , 3s3p 3 , 3s 2 3p3d, 3s 2 3p4s, 3s 2 3p4p and 3s 2 3p4d, giving rise to 1378 individual lines, and is undertaken using the recently developed RMATRX II plus FINE95 suite of codes. A detailed comparison is made with a previous R-matrix calculation and significant differences are found for some transitions. The atomic data are subsequently incorporated into the modeling code cloudy to generate line intensities for a range of plasma parameters, with emphasis on allowed UV and EUV emission lines detected from the Io plasma torus. Electron density-sensitive line ratios are calculated with the present atomic data and compared with those from CHIANTI v7.1, as well as with Io plasma torus spectra obtained by FUSE and EUVE. The present line intensities are found to agree well with the observational results and provide a noticeable improvement upon the values predicted by CHIANTI.
Bulletin of the American Physical Society, 2016
We present a comprehensive study of electron collisions with boron atoms by using the B-spline R-... more We present a comprehensive study of electron collisions with boron atoms by using the B-spline R-matrix method for electron energies ranging from threshold to 100 eV. Elastic, excitation, and ionization cross sections were obtained for all transitions between the lowest 11 states of boron. A multiconfiguration Hartree-Fock method with nonorthogonal term-dependent orbitals was employed to generate accurate wave functions for the target states. Close-coupling expansions including 13, 51, and 999 physical and pseudo target states of boron were used to check the sensitivity of the results to changes in the theoretical model. The cross-section dataset obtained from the large-scale calculations is expected to be sufficiently accurate and comprehensive for most current modeling applications involving neutral boron.
Bulletin of the American Physical Society, 2008
Bulletin of the American Physical Society, 2009
Experimental and theoretical collisional excitation cross sections are reported for the transitio... more Experimental and theoretical collisional excitation cross sections are reported for the transitions 3s(exp 2)3p(exp 3)4S(exp o) approaches 3s(exp 2)3p(exp 3) 2D(exp o), 2P(exp o), and 3s3P(exp 4) 4P in S II. The transition wavelengths (energies) are 6716 A (1.85 eV), 4069 A (3.05 eV), and 1256 A (9.87 eV), respectively. In the experiments, use is made of the energy-loss merged-beams method. The metastable fraction of the S II beam was assessed and minimized. The contribution of elastically scattered electrons was reduced by the use of a lowered solenoidal magnetic field and a modulated radio-frequency voltage on the analyzing plates and by retarding grids to reject the elastically scattered electrons with larger Larmor radii. For each transition, comparisons are made among experiments, the new 19 state R-matrix calculation, and three other close-coupling calculations.
The Astrophysical Journal, 2011
New extensive calculations are reported for electron collision strengths, rate coefficients, and ... more New extensive calculations are reported for electron collision strengths, rate coefficients, and transition probabilities for the astrophysically important lines of Fe VIII. 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 102 fine-structure levels of Fe VIII covering all possible terms of the ground 3p 63d and singly excited 3p 53d 2, 3p 64l, 3p 53d4s, 3s3p 63d 2, and 3p 65l configurations. The present calculations are more extensive than the previous ones, leading to a total 5151 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 tran...
Collision strengths for transitions between the 3s23p4 P2, 1, 03, 1D2, and 1S0 levels and from th... more Collision strengths for transitions between the 3s23p4 P2, 1, 03, 1D2, and 1S0 levels and from these levels to the 3s3p5 P02, 1, 03 and 1P01 levels of Fe XI are calculated using a semirelativistic R-matrix approach. The 38 fine-structure levels arising from the 20 LS 3s23p4 P3, 1D, 1S, 3s3p5 P03, 1P0, 3s23p3(4S0)3d D03, 3s23p3(2P0)3d P01,3, 1, 3D0, 1, 3F0, 3s23p3(2D0)3d S01,3, 1, 3P0, 1, 3D0, 1, 3F0 states are included in our calculation. These 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. Complicated resonance structures are found to enhance the collision strengths significantly for many transitions in the threshold energy regions. Our collision strengths are compared with the available results of Bhatia & Doschek at 8.0, 16.0, and 24.0 ryd. The collision strengths are integrated o...