E1 oscillator strengths and transition rates among levels of Cl I

We present oscillator strengths and transition rates of E1 transitions between the fine-structure levels belonging to the configurations 3s23p5, 3s3p6, and 3s23p4nl, where nl= 4s, 5s, 6s, 4p, 5p, 3d, 4d. The calculations have used extensive configuration interaction (CI) wavefunctions, with the associated Hamiltonian matrix adjusted to ensure that the eigenenergies agree with experimental energy level data ('fine tuning'). There are consequential small changes in the CI mixing coefficients from their ab initio values and these corrected coefficients are used in the calculation of the transition data. The method of optimization of the orbital radial functions (expressed in terms of Slater-type orbitals) is described and the radial function parameters are also presented. We show some comparisons between our work and those of earlier calculations and demonstrate how the inclusion of relativistic effects (which we achieve through the use of the Breit-Pauli approximation) can result in a substantial redistribution of the oscillator strength from the LS calculation. We also demonstrate that the fine-tuning process can make, particularly for intercombination lines, a substantial improvement in the agreement between theoretical and experimental oscillator strengths.