Dielectronic recombination rate coefficients for the CoI isoelectronic sequence

Abstract

In our recent reports (2007 J. Phys. B: At. Mol. Opt. Phys. 40 4269–86 and 2008 J. Quant. Spectrosc. Radiat. Transfer 109 2000–2008), we performed detailed and large-scale ab initio calculations on the total dielectronic recombination (DR) rate coefficients for Co-like gold and tungsten. Here we extend the calculations for another eight ions (Kr9+, Mo15+, Ag20+, Xe27+, Pr32+, Dy39+, At58+ and U65+) along the CoI isoelectronic sequence in the ground state employing the flexible atomic code. The total DR rates mainly come from complex series 3d84ln′l′ and 3p53d94ln′l′. The complex series 3p53d10n′l′ and 3d85ln′l′ also contribute significantly at low (<0.1EI, EI is the ionization energy of the corresponding Ni-like ions) and high (>1.0EI) electron temperatures, respectively. On the basis of the calculated results, a general analytic formula for the total DR rate coefficients of all the ions along the CoI isoelectronic sequence is constructed. This formula can generally reproduce the calculated DR rate coefficients to within 3% for electron temperatures above 0.1EI. Comparisons of the present results with those obtained from the commonly used Burgess–Merts (BM) semiempirical formula show that the BM formula is not adequate to predict the total DR rate coefficients at relatively low electron temperatures and for low-Z ions. In addition, the total DR rate coefficients from the first excited state are also presented.