Effective collision strengths for electron impact excitation of C II

Abstract

We extend a previous calculation of effective collision strengths for electron impact excitation of the boron-like ion C . The earlier work was restricted to the excitation within the 2s 2 2p ground configuration and the sixteen 2s 2 2p-2s2p 2 fine-structure transitions whilst the present paper considers all fine-structure transitions among the levels arising from the lowest 16 LS states. The collisional cross sections are computed in the multichannel close-coupling R-matrix approximation, in which sophisticated configuration-interaction wave functions are used to represent the target states. The 16 states included have the following basis configurations: the 2s 2 2p ground state, four 2s2p 2 states, three 2p 3 states, one 2s2p3s state as well as the 2s 2 3l(l = s, p, d) and 2s 2 4l(l = s, p, d, f) states. The 16 LS target states correspond to 30 fine-structure levels and lead to a total of 435 fine-structure transitions. In this paper we tabulate effective collision strengths, obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities, for electron temperatures in the range given by log10 Te(K) = 3.0−5.5, suitable for most astrophysical applications and laboratory plasma diagnostics. Significant differences from a previous calculation are noted and comparisons are made with some recent experimental data.