Effective Collision Strengths and Radiative Parameters for Lines in the Sc ii Spectrum

Abstract

Abstract This work reports large-scale calculations of electron excitation effective collision strengths and transition rates for a wide range of Sc ii spectral lines for astrophysical analysis and modeling. The present results are important for reliable abundance determinations in various astrophysical objects, including metal-poor stars, H ii regions, and gaseous nebulae. Accurate descriptions of the target wave functions and adequate accounts of the various interactions between the target levels are of primary importance for calculations of collision and radiative parameters. The target wave functions have been determined by a combination of the multiconfiguration Hartree–Fock and B-spline box-based close-coupling methods, together with the nonorthogonal orbitals technique. The calculations of the collision strengths have been performed using the B-spline Breit–Pauli R-matrix method. The close-coupling expansion includes 145 fine-structure levels of Sc ii belonging to the terms of the 3p 63d 2, 3p 63d4l (l = 0–3), 3p 63d5l (l = 0–3), 3p 63d6s, 3p 64s 2, 3p 64s4l (l = 0–3), 3p 64s5l (l = 0–1), and 3p 64p 2 configurations. The effective collision strengths are reported as a function of electron temperature in the range from 103 to 105 K. The collision and radiative rates are reported for all of the possible transitions between the 145 fine-structure levels. Striking discrepancies exist with the previous R-matrix calculations of the effective collision strengths for the majority of the transitions, indicating possible systematic errors in these calculations. Thus, there is a need for accurate calculations to reduce the uncertainties in the atomic data. The likely uncertainties in our effective collision strengths and radiative parameters have been assessed by means of comparisons with other collision calculations and available experimental radiative parameters.