Simulation of atomic transition arrays for opacity calculations

A method is proposed for simulating resolved transition arrays of ionized atom spectra in full intermediate coupling. The wave number and intensity of each line in an array are picked at random from separated but correlated distributions. Even though each line is not exactly reproduced, this procedure yields the correct following characteristics of the supposedly symmetric array: total intensity; second and fourth moments of the distributions of unweighted wave numbers, of intensity-weighted wave numbers, and of transition amplitudes; numbers of lines and sums of intensities in consecutive narrow energy ranges. All the parameters of the distribution are obtained by means of compact formulas, or tabulated. Applications to the arrays 4d4-4d35p of Pd6+ and 4d75s-4d75p of Cd4+ are presented. Comparison with the explicit results of the Slater-Condon method shows good agreement. It is proposed to use this method for fast and reliable computation of Rosseland means and other opacity properties.