General analytic formula for total dielectronic recombination rate coefficients of Ni-like ions

A general analytic formula for the total dielectronic recombination (DR) rate coefficients of all the ions along the NiI isoelectronic sequence with $34<~Z<~92$ is constructed on the basis of previously calculated DR data, which were obtained by relativistic ab initio level-by-level computations using the HULLAC code for ten Ni-like ions. The DR rate coefficients are given as a function of the electron temperature and of the ion charge. The results generated by this formula reproduce the previously calculated DR rate coefficients, generally to better than 5% accuracy for all electron temperatures ${\mathrm{kT}}_e>~{0.03E}_I$ ${(E}_I$ is the ionization energy of the Cu-like ion). As a test, the results of level-by-level DR calculations for two additional elements, barium and tungsten, are compared to those of the analytic formula. The agreement is found to be similar to that for the first ten ions. The analytic formula may be conveniently used for modeling the ion abundance distribution in hot plasmas.