Electron impact excitation of N IV: calculations with the DARC code and a comparison with ICFT results

Abstract

There have been discussions in the recent literature regarding the accuracy of the available electron impact excitation rates (equivalently effective collision strengths ${\rm Y}$) for transitions in Be-like ions. In the present paper we demonstrate, once again, that earlier results for ${\rm Y}$ are indeed overestimated (by up to four orders of magnitude), for over 40\% of transitions and over a wide range of temperatures. To do this we have performed two sets of calculations for N~IV, with two different model sizes consisting of 166 and 238 fine-structure energy levels. As in our previous work, for the determination of atomic structure the GRASP (General-purpose Relativistic Atomic Structure Package) is adopted and for the scattering calculations (the standard and parallelised versions of) the Dirac Atomic R-matrix Code ({\sc darc}) are employed. Calculations for collision strengths and effective collision strengths have been performed over a wide range of energy (up to 45~Ryd) and temperature (up to 2.0$\times$10${}^6$~K), useful for applications in a variety of plasmas. Corresponding results for energy levels, lifetimes and A-values for all E1, E2, M1 and M2 transitions among 238 levels of N~IV are also reported.

This paper with 5 Figs. and 8 Tables will appear in MNRAS (2016)

References in corpus (4)

• Ultraviolet Emission Lines in Young Low Mass Galaxies at z~2: Physical Properties and Implications for Studies at z>7
• Energy levels, radiative rates and electron impact excitation rates for transitions in Fe XIV
• Electron impact excitation of Be-like ions: a comparison of DARC and ICFT results
• Energy levels, radiative rates and electron impact excitation rates for transitions in C III

Cited by in corpus (4)

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• Electron-impact excitation of N${}^{3+}$ using the B-spline R-matrix method: Importance of the target structure description and the size of the close-coupling expansion
• Uncertainties on atomic data. A case study: N IV
• Discrepancies in Atomic Data and Suggestions for their Resolutions