COLLISION STRENGTHS AND EXCITATION RATE COEFFICIENTS FOR TRANSITIONS IN CA-XV

Collision strengths among fine-structure levels of the 1s(2)2S(2)2p2, 1s(2)2s2p3, and 1s(2)2p4 configurations of Ca XV have been computed in the j-j coupling scheme using the Dirac-Fock R-matrix program. All partial waves with J less-than-or-equal-to 29/2 are included, and collision strengths have been computed on a dense energy grid in order to elucidate the resonances. The results are tabulated in a wide energy range below 200 Ry. Contributions of the relativistic effects are assessed and comparisons are made with the earlier available collision strengths. Agreement with the available values, at electron energies above thresholds, is good for most of the transitions, but striking differences (of up to an order of magnitude) are noticed for some of the transitions. Effective collision strengths are also obtained after integrating collision strengths over a Maxwellian distribution of electron velocities, and these are tabulated at a number of temperatures below 10(7) K. Comparisons are made with the earlier effective collision strengths obtained with the R-matrix method. Although the present results are comparable with the earlier effective collision strengths for most of the transitions. differences of up to a factor of 3 are observed for some of the transitions at temperatures below 10(6) K.