Oscillator strengths for transitions among quartet states in Cr II

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Abstract
Approximately 150 dipole oscillator strengths are calculated in LS coupling for transitions between low-lying quartet terms of the configurations 1s22s22p63s23p63d5, 1s22s22p63s23p63d4-4s and -4p and 1s22s22p63s23p63d34s2 in Cr II. Difficulties arise in the calculation from the occurrence of several-up to six-terms of a given configuration having different parentage and which are more or less strongly mixed. It is important that the mixing coefficients be reasonably good in order to obtain reliable oscillator strengths. An ab initio R-matrix calculation has been performed with corrections applied to the relative energies of the parent terms. Application of these corrections has in many cases a dramatic effect on computed transition strengths. The success of this approach, which uses relatively simple wavefunctions, and the sensitivity of the results to the adjustments and to other factors such as relativistic effects, which are not included, are discussed. Comparisons with available observed values for the oscillator strengths and lifetimes are included.