Dielectronic recombination process in laser-produced tantalum plasmas

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Abstract
The 3d-4f and 3d-5f emission patterns occurring between 4.5 and 6.5 Å in the spectra of laser-produced plasmas of highly ionized tantalum are studied, and the pseudocontinuum which underlies the former is interpreted. For the transition subarrays suspected to be responsible for the pseudocontinuum, the average wavelengths and widths are computed ab initio in the formalism of spin-orbit-split arrays; these subarrays are proven to cover a continuous band of wavelengths. For their intensities, the dielectronic recombination (DR) process populates efficiently the upper configurations, which, in most cases, lie above the ionization levels. The autoionization and radiative-transition probabilities, and the DR coefficients, are computed ab initio, in the form of averages for whole configurations or subconfigurations of Cu-like tantalum. The compact formulas for these averages are valid in intermediate coupling, avoiding any diagonalization. All the needed radial integrals are computed by means of a relativistic parametric potential central-field code.