arXiv subjects

K M Aggarwal

Publications and source records attributed to K M Aggarwal.

At least 19 recordsLinked to original sources

arXiv2021

Electron Impact Excitation of O III: An Assessment

Tayal and Zatsarinny [Astrophys. J. 850 (2017) 147] have reported results for energy levels, radiative rates (A-values), lifetimes, and effective collision strengths ($Υ$) for transitions among 202 levels of C-like O~III. For the calculations they have adopted the multi-configuration Hartree-Fock (MCHF) code for the energy levels and A-values, and B-spline $R$-matrix (BSR) code for $Υ$. Their reported results cover a (much) larger range of levels/transitions than generally available in the literature, and appear to be accurate for energy levels and A-values. However, the magnitude and behaviour of $Υ$ do not appear to be correct for several transitions. We demonstrate this through our independent calculations by adopting the flexible atomic code (FAC) and recommend a fresh calculation for this important ion.

physics.atom-ph↗

arXiv2019

Comment on "Energy levels, oscillator strengths, and transition probabilities for sulfur-like scandium, Sc~VI" by El-Maaref et al.\, [Indian J. Phys. {\bf 91} 1029 (2017)]

In this comment, through our independent calculations, we assess that the recently reported results of El-Maaref et al. [{\em Indian J. Phys.} {\bf 91} 1029 (2017)] for energy levels, oscillator strengths, radiative rates, and lifetimes are inaccurate and unreliable for several levels and transitions of S-like Sc~VI.

physics.atom-ph↗

arXiv2019

Comment on "Atomic structure and excitation cross section by electron impact of tungsten ions, W$^{38+}$" by El-Maaref et al [J. Phys. B 52(2019) 065202]

Recently, El-Maaref {\it et al}\, [J. Phys. B 52(2019) 065202] have reported results for energy levels, radiative rates and collision strengths ($Ω$) for some transitions of Kr-like W~XXXIX. For the calculations of these parameters they have adopted several codes, including GRASP, DARC and FAC. For energy levels they have shown discrepancies of up to 1.64~Ryd between the GRASP and FAC calculations, whereas for $Ω$ the differences between the DARC and FAC results are over an order of magnitude for a few transitions. In addition, for several transitions there is an anomaly in the behaviour of $Ω$ between the two sets of calculations. In this comment, we demonstrate that their results from both codes are incorrect, and hence cannot be relied upon.

physics.atom-ph↗

arXiv2019

Electron Impact Excitation of S III: an Assessment

In a recent paper, Tayal et al. [{\em Astrophys. J. Suppl.} {\bf 2019}, {\emph 242}, 9] have reported results for energy levels, radiative rates (A-values) and effective collision strengths ($Υ$) for transitions among the 198 levels of Si-like S~III. For the calculations they have adopted the multi-configuration Hartree-Fock (MCHF) code for the energy levels and A-values, and B-spline $R$-matrix (BSR) code for $Υ$. Their reported results appear to be accurate for energy levels and A-values, but not for $Υ$. Through our independent calculations by adopting the flexible atomic code (FAC), we demonstrate that their reported results for $Υ$ are underestimated, by up to a factor of two, and at all temperatures, particularly for the allowed transitions, but some forbidden ones too. Additionally, for transitions involving the higher levels the behaviour of their $Υ$ results is not correct.

astro-ph.SR↗

arXiv2019

Comment on "Configuration interaction calculations and excitation rates of X-ray and EUV transitions in sulfurlike manganese" by El-Maaref et al. [J. Elect. Spectrosc. Related Phen. 215 (2017) 22]

In one of the papers, El-Maaref et al. [J. Elect. Spectrosc. Related Phen. 215 (2017) 22] have reported results for energy levels, oscillator strengths (f-values), radiative rates (A-values), collision strengths ($Ω$), and excitation rates for transitions in S-like Mn~X. However, except for energy levels their results are restricted to only a few transitions and hence have limited application. Furthermore, most of their results have scope for improvement, but for $Ω$ are not correct as these have been found to be overestimated by an order of magnitude. In this comment we discuss the discrepancies and deficiencies of their results and recommend that a fresh calculation should be performed for this ion.

physics.atom-ph↗

arXiv2019

Comment on "Electron impact excitation and ionization cross section of tungsten ions, W$^{44+}$" by El-Maaref et al. [J. Quant. Spectrosc. Radiat. Transfer 2019, 224:147]

In a recent paper, El-Maaref et al. [J. Quant. Spectrosc. Radiat. Transfer 2019, 224:147] have reported atomic data for Zn-like W~XLV. Their results are mainly for energy levels, radiative rates, collision strengths ($Ω$) for electron impact excitation, and cross sections for ionization, but for only for a few levels/transitions, and in a very limited range of energy. For the calculations of $Ω$ they have adopted the DARC code. In this comment, through our independent calculations, we demonstrate that their results for $Ω$ are highly underestimated by over two orders of magnitude, and hence are totally unreliable.

physics.atom-ph↗

arXiv2019

Radiative rates for E1, E2, M1, and M2 transitions in F-like ions with 12 <= Z <= 23

In this paper, energy levels, radiative rates and lifetimes are reported for 11 F-like ions with 12 $\le$ Z $\le$ 23. Up to 198 levels (depending on the ion) have been considered which include 113 of the 2s$^2$2p$^5$, 2s2p$^6$, 2s$^2$2p$^4$3$\ell$, 2s2p$^5$3$\ell$, and 2p$^6$3$\ell$ configurations. The general-purpose relativistic atomic structure package ({\sc grasp}) and the flexible atomic code ({\sc fac}) have been adopted for calculating the energy levels, but the {\sc grasp} alone for the remaining parameters. Radiative rates (along with oscillator strengths and line strengths) are listed for all E1, E2, M1, and M2 transitions of the ions. Comparisons are made with earlier available theoretical and experimental energies, for all ions, in order to assess the accuracy of the calculations. Comparisons have also been made for the radiative rates and lifetimes, which have been possible for only those among the lowest 60 levels.

physics.atom-ph↗

arXiv2018

Comment on "Collision strength and effective collision strength for Br~XXVII" by Goyal et al. [Can. J. Phys. 95 (2017) 1127]

In a recent paper, Goyal et al. [Can. J. Phys. {\bf 95} (2017) 1127] have reported results for collision strengths ($Ω$) and effective collision strengths ($Υ$) for transitions among the lowest 52 levels of F-like Br~XXVII. For their calculations, they have adopted the Dirac atomic $R$-matrix code (DARC) and the flexible atomic code (FAC). In this comment we demonstrate that their results for both parameters are erratic, inaccurate, and unreliable.

physics.atom-ph↗

arXiv2018

Comment on "Collision strength and effective collision strength for Ba~XLVIII" by Mohan et al. [Can. J. Phys. 95 (2017) 173]

In a recent paper, Mohan et al. [Can. J. Phys. {\bf 95} (2017) 173] have reported results for collision strengths ($Ω$) and effective collision strengths ($Υ$) for transitions from the ground to higher 51 excited levels of F-like Ba~XLVIII. For the calculations of $Ω$, the Dirac atomic $R$-matrix code (DARC) and the flexible atomic code (FAC) have been adopted, in order to facilitate a direct comparison. However, for the subsequent calculations of $Υ$, DARC alone has been employed. In this comment, we demonstrate that while their limited results for $Ω$ are comparatively reliable, for $Υ$ are not, particularly for the allowed transitions and at lower temperatures. Apart from the non expected behaviour, their $Υ$ values are overestimated for several transitions, by about a factor of two.

physics.atom-ph↗

arXiv2018

Radiative rates for E1, E2, M1, and M2 transitions in Ne-like Hf LXIII, Ta LXIV and Re LXVI

Calculations for energy levels, radiative rates and lifetimes have been performed for three Ne-like ions, namely Hf~LXIII, Ta LXIV and Re LXVI, for which the general-purpose relativistic atomic structure package (GRASP) has been adopted. Results are presented among the lowest 121 levels of these ions, which belong to the 2s$^2$2p$^6$, 2s$^2$2p$^5$3$\ell$, 2s2p$^6$3$\ell$, 2s$^2$2p$^5$4$\ell$, 2s2p$^6$4$\ell$, and 2s$^2$2p$^5$5$\ell$ configurations, but CI (configuration interaction) has been considered among a much larger number of levels. No measurements for energy levels are available but comparisons have been made with the earlier similar theoretical results. Additionally, calculations have also been performed with the flexible atomic code (FAC) in order to assess the effect of (much) larger CI on energy levels.

physics.atom-ph↗

arXiv2018

Comment on "Atomic data for Ne-like ions useful in plasma diagnostic" by Singh et al. [Can. J. Phys. 96 (2018) 36]

In a recent paper, Singh et al. [Can. J. Phys. {\bf 96} (2018) 36] have reported results for energy levels, radiative rates, and lifetimes among 209 levels of four Ne-like ions, namely Hf~LXIII, Ta~LXIV, W~LXV, and Re~LXVI. For their calculations, they have adopted the GRASP and FAC codes, and have assessed their energy levels to be accurate to $\sim$0.5~Ryd, based on comparisons between the two sets of energies. However, some of the levels between the two calculations differ by up to $\sim$2~Ryd, and for three ions. In addition, we also note that some of their results with FAC cannot be reproduced, and hence the large discrepancies.

physics.atom-ph↗

arXiv2018

Comment on "Energy levels and radiative rates for Ne-like ions from Cu to Ga" by N.~Singh and S.~Aggarwal [Pramana -- J. Phys. 89 (2017) 79]

Recently, N.~Singh and S.~Aggarwal [Pramana -- J. Phys. 89 (2017) 79] have reported energies and lifetimes for 127 levels of three Ne-like ions, namely Cu~XX, Zn~XXI and Ga~XXII. For the calculations they have adopted two independent atomic structure codes, i.e. GRASP and FAC, and have concluded that both codes give comparable energies. However, we find that the differences between the two sets of energies are up to 1.5~Ryd (over 1.6$\times$10$^5$ wavenumbers) for many levels, and for all three ions. In the absence of other available theoretical or experimental data, it becomes difficult to know which set of energies is more accurate. Through our calculations with the same code we demonstrate that their listings from the FAC calculations are incorrect. A few more anomalies noted in their tabulated results are also highlighted.

physics.atom-ph↗

arXiv2018

Radiative rates for E1, E2, M1, and M2 transitions in Ne-like Cu XX, Zn XXI and Ga XXII

Energy levels, radiative rates and lifetimes are reported for the lowest 139 levels of three Ne-like ions, namely Cu~XX, Zn~XXI and Ga~XXII. These levels mostly belong to the 2s$^2$2p$^6$, 2s$^2$2p$^5$3$\ell$, 2s2p$^6$3$\ell$, 2s$^2$2p$^5$4$\ell$, 2s2p$^6$4$\ell$, and 2s$^2$2p$^5$5$\ell$ configurations. For the calculations the general-purpose relativistic atomic structure package (GRASP) has been adopted. Comparisons are made with earlier available theoretical and experimental results, particularly among the lowest 27 levels of the 2s$^2$2p$^6$ and 2s$^2$2p$^5$3$\ell$ configurations. Due to paucity of similar data for higher lying levels, analogous calculations have also been performed with the flexible atomic code (FAC). These calculations help in assessing the accuracy of our calculated results, especially for the energy levels.

physics.atom-ph↗

arXiv2018

Radiative rates for E1, E2, M1, and M2 transitions in F-like ions with 55 <= Z <= 73

Energy levels, radiative rates and lifetimes are reported for 19 F-like ions with 55 $\le$ Z $\le$ 73, among 113 levels of the 2s$^2$2p$^5$, 2s2p$^6$, 2s$^2$2p$^4$3$\ell$, 2s2p$^5$3$\ell$, and 2p$^6$3$\ell$ configurations. The general-purpose relativistic atomic structure package (GRASP) has been adopted for the calculations, and radiative rates (and other associated parameters, such as oscillator strengths and line strengths) are listed for all E1, E2, M1, and M2 transitions of the ions. Comparisons are made with earlier available theoretical and experimental energies, especially for Ba~XLVIII. Nevertheless, calculations have also been performed with the flexible atomic code (FAC), and with a much larger configuration interaction with up to 38~089 levels, for further accuracy assessments, particularly for energy levels.

physics.atom-ph↗

arXiv2016

Energy levels, radiative rates and electron impact excitation rates for transitions in Si III

Energy levels and radiative rates (A-values) for four types of transitions (E1, E2, M1, and M2) are reported for an astrophysically important Mg-like ion Si~III, whose emission lines have been observed in a variety of plasmas. For the calculations, well-known and widely-used GRASP code has been adopted, and results are listed for transitions among the 141 levels of the 3$\ell3\ell'$ and 3$\ell$4$\ell$ configurations. Experimental energies are available for only the lowest 58 levels but there is no major discrepancy with theoretical results. Similarly, the A-values and lifetimes show a satisfactory agreement with other available results, particularly for strong E1 transitions. Collision strengths are also calculated, with the DARC code, and listed for resonance transitions over a wide energy range, up to 30~Ryd. No similar results are available in the literature for comparisons. However, comparisons are made with the more important parameter, effective collision strength ($Υ$), for which recent $R$-matrix results are available for a wide range of transitions, and over a large range of temperatures. To determine $Υ$, resonances have been resolved in a narrow energy mesh, although these are not observed to be as important as for other ions. Unfortunately, large discrepancies in $Υ$ values are noted for about half the transitions. The differences increase with increasing temperature and worsen as the upper level J increases. In most cases the earlier results are overestimated, by up to (almost) two orders of magnitude, and this conclusion is consistent with the one observed earlier for Be-like ions.

physics.atom-ph↗

arXiv2016

Electron impact excitation rates for transitions in Mg V

Energy levels, radiative rates (A-values) and lifetimes, calculated with the GRASP code, are reported for an astrophysically important O-like ion Mg~V. Results are presented for transitions among the lowest 86 levels belonging to the 2s$^2$2p$^4$, 2s2p$^5$, 2p$^6$, and 2s$^2$2p$^3$3$\ell$ configurations. There is satisfactory agreement with earlier data for most levels/transitions, but scope remains for improvement. Collision strengths are also calculated, with the DARC code, and the results obtained are comparable for most transitions (at energies above thresholds) with earlier work using the DW code. In thresholds region, resonances have been resolved in a fine energy mesh to determine values of effective collision strengths ($Υ$) as accurately as possible. Results are reported for all transitions at temperatures up to 10$^6$~K, which should be sufficient for most astrophysical applications. However, a comparison with earlier data reveals discrepancies of up to two orders of magnitude for over 60\% of transitions, at all temperatures. The reasons for these discrepancies are discussed in detail.

physics.atom-ph↗

arXiv2016

Comment on "Atomic structure calculations for F-like tungsten" by S. Aggarwal

Recently, S. Aggarwal [Chin. Phys. B 23 (2014) 093203] reported energy levels, radiative rates and lifetimes for the lowest 60 levels belonging to the 2s$^2$2p$^5$, 2s2p$^6$ and 2s$^2$2p$^4$3$\ell$ configurations of F-like tungsten. There is no discrepancy for his calculated energies for the levels and the radiative rates for the limited number of E1 transitions, but the reported results for lifetimes are highly inaccurate. According to our calculations, errors in his reported lifetimes are up to 6 orders of magnitude for several levels. Here we report the correct lifetimes for future comparisons and applications, and also explain the reason for discrepancies.

physics.atom-ph↗

arXiv2016

Comment on "Relativistic atomic data for W XLVII" by S. Aggarwal {\em et al.} [Chin. Phys. B 24 (2015) 053201]

Recently, S. Aggarwal et al. [Chin. Phys. B 24 (2015) 053201] reported energy levels, radiative rates and lifetimes for the lowest 148 levels belonging to the 3s$^2$3p, 3s3p$^2$, 3s$^2$3d, 3s3p3d, 3p$^3$, 3p$^2$3d, 3s3d$^2$, 3p3d$^2$, and 3d$^3$ configurations of Al-like tungsten. While their calculated energies for the levels and the radiative rates for transitions are correct, the reported results for lifetimes are completely wrong. According to our calculations, errors in their reported lifetimes are up to 14 orders of magnitude for over 90\% of the levels. Here we report the correct lifetimes and explain the reasons for discrepancies.

physics.atom-ph↗