A statistical approach for simulating detailed-line spectra

A general statistical model for simulating electric-dipolar lines in complex spectra of LTE or NLTE plasmas is presented. In this model, each transition array is represented by a pair of Gaussian subarrays, whose characteristics (average wavenumbers, strength distributions, and numbers of lines) change in a continuous way from LS (where one subarray vanishes) to jj coupling. The transition amplitude and the two-level energies of each line are picked at random in a joint triple distribution that takes into account the correlation between the line strengths and energies. This insures that the first and the second strength-weighted moments of the line energies are equal to those obtained in the DLA approach. Examples of application to the calculation of Rosseland and Planck mean opacities are given (Fe plasma in LTE, for Te = 20 eV and ρ = 10-2, 10-3, 10-4 g cm-3) which show very good agreement with the OPAL values