Transitions in Ar II

The authors present extensive configuration interaction (CI) calculations of oscillator strengths, transition probabilities and lifetimes of upper levels of all transitions in Ar II between the levels of 3s 2 3p 5 , 3s3p 6 , 3p 4 3d, 3p 4 4s and 3p 4 4p states. The calculations incorporate the major correlation effects and in addition allow for the orbital functions (particularly 3p) to be effectively different for different states. Some discrepancies with experimental energies remain, particularly those of levels with a 3p 4 1 S core. Prior to the calculation of the oscillator strengths, the authors 'fine-tune' the CI coefficients using experimental energies. Specifically, the final CI coefficients are determined following small adjustments to the diagonal Hamiltonian matrix elements so that the calculated eigenvalue differences agree with the corresponding experimental energy separations. The work describes in detail previous calculations of quartet levels and extends the calculations to other symmetries. Comparison with recent, highly accurate cascade-free experiments shows close accord in all but a small number of transitions.