DECAY-RATES AND LIFETIMES OF THE 4P (6,4)P(J)(O) AND 4P (6)D(J)(O) LEVELS OF CR-II

Transition rates have been calculated for all electric dipole allowed decays for Cr II of the 3d(4)4p levels arising from the closely spaced P-6(o), 6D(o) and P-4(o) terms, to all lower levels that arise from the 6S, 6D, 4P, and 4D terms of the 3d5 and 3d(4)4s configurations. We have applied a recently developed method of selecting a 'natural' basis for the algebraic expansion of the spectroscopic states that results in a very substantial reduction in the size of the problem, and hence contributes significantly towards rendering the problem at all tractable. To our knowledge, no previous ab initio calculations exist that explore these decays involving the even quartets with a serious consideration of both configuration interaction and relativistic effects. Our calculations include corrections to give the correct observed splittings for closely spaced levels in each J P subspace, and corrections for the difference between calculated and observed transition energies have also been applied. Based on the calculated transition rates, we have further determined the lifetimes of the 4p P-6,4(J)o, and 4p 6D(J)o levels of the Cr II ion, and compared them with available observed values. The agreement with the recent experiments of Schade et al is reasonably satisfactory, whereas comparison with some of the older work shows larger discrepancies.