Electron-impact excitation of Fe4+: an intermediate-coupling R-matrix calculation

Abstract

For a number of years, there has been a major effort to calculate electron-impact excitation data for every ion stage of iron embodied by the ongoing efforts of the IRON project by Hummer et al (1993 Astron. Astrophys. 279 298). Due to the complexity of the targets, calculations for the lower stages of ionization have been limited to either intermediate-coupling calculations within the ground configurations or LS-coupling calculations of the ground and excited configurations. However, accurate excitation data between individual levels within both the ground and excited configurations of the low charge-state ions are urgently required for applications to both astrophysical and laboratory plasmas. Here we report on the results of the first intermediate-coupling R-matrix calculation of electron-impact excitation for Fe4+ for which the close-coupling (CC) expansion includes not only those levels of the 3d4 ground configuration, but also the levels of the 3d34s, 3d34p, 3d34d and 3d24s2 excited configurations. With 359 levels in the CC expansion and over 2400 scattering channels for many of the JΠ partial waves, this represents the largest electron–ion scattering calculation to date and it was performed on massively parallel computers using a recently developed set of relativistic parallel R-matrix programs.