Oscillator strengths for transitions among sextet states in Cr II

Abstract

Oscillator strengths for transitions among sextet terms of the configurations 3d5, 3d44s, 3d44p, 3d44d and 3d45s of singly ionized Chromium have been calculated. Transition wavelengths lie in the range 2050-3100 A. The calculations have been performed in two independent ways: One uses the Multiconfiguration Optimized Potential Model (MCOPM) and the other uses an R-matrix model in which the target wave functions are obtained from the MCOPM. Some difficulties that arise in calculations involving the open 3d shell are detailed. The main purpose is to obtain data of a relatively high degree of reliability. Comparison of the results as well as estimates of numerical cancellation effects in the MCOPM calculation indicate that they should be accurate to 10% or better with some exceptions where relativistic effects not included in the present calculations may be important. The results provide a useful benchmark for comparison with experimental results since, in the present theoretical work, we do not generally encounter the difficulties of near degeneracies among terms with the same L and S that turn up in other symmetries for this ion. Comparison with observations available at present are given.