1 Introduction

This is a continuation of our efforts to generate atomic data (energy levels, oscillator strengths, radiative rates, collision strengths, and excitation rates) for C-like ions. Several papers have been published over the past two decades reporting such data, particularly for energy levels and radiative rates. To summarise, these papers are by Aggarwal et al. (1997a) for O III, Aggarwal et al. (1997b) for Ca XV and Fe XXI, Aggarwal (1998) for Ne V, Mg VII, Si IX and S XI, and Aggarwal et al. (2001) for F IV, Na VI, Al VIII, P X, Cl XII and Ar XIII. In the present paper we report similar data for six other C-like ions, namely K XIV, Sc XVI, Ti XVII, V XVIII, Cr XIX and Mn XX. This work completes the sequence for ions with nuclear charges $8 \le Z \le 26$.

Emission lines of C-like ions are highly useful as diagnostics of solar, astrophysical and fusion plasmas, the interpretation of which requires the knowledge of atomic parameters. Emission lines of the ions for which we present data in this paper have already been observed (Kelly 1987). Therefore, a few researchers in the past have reported atomic data for C-like ions. However, most of the calculations have been confined to the lowest 20 levels of the (1s²) 2s²2p², 2s2p³ and 2p⁴ configurations. Similar data for transitions among the levels of the 2s²2p3s, 2s²2p3p and 2s²2p3d configurations, which mostly lie in the X-ray and EUV regions, are equally important, especially for the modeling of astrophysical and laboratory plasmas, and therefore have become increasingly in demand. Fawcett (1987) has included levels of the 2s²2p3s and 2s²2p3d configurations in his calculations, whereas Zhang & Sampson (1996, 1997) have also included levels of the 2s²2p3p configuration. Both Fawcett and Zhang & Sampson have included configuration interaction (CI) and relativistic effects (RE) in their calculations, as these are equally important particularly for the ions under discussion here. However, atomic data have been reported for a few transitions only, and therefore, our aim is to report results of oscillator strengths and radiative rates for all allowed transitions among 46 fine-structure levels of the (1s²) 2s²2p², 2s2p³, 2p⁴, 2s²2p3s, 2s²2p3p and 2s²2p3d configurations. Additionally, we find that there is scope for improvement over the earlier results, because the inclusion of CI in these calculations is rather restricted.