A two-step collisional-radiative model for interpreting spectra originating from autoionizing levels

A two-step collisional-radiative model is proposed for describing spectra which arise from radiative decays from autoionizing levels. In this procedure only two adjacent ionization states are considered at a time, and the ratio of the ionic populations is taken to be a free parameter. The other free parameters are the electron temperature and density. In the first step of the model, the populations of the ground and singly excited levels of the two ionization states are determined by solving two separate sets of collisional radiative rate equations; one set for each ionization state. In the second step, the populations of the doubly excited levels are calculated using the results of the first step. Radiative trapping effects are taken into account using the mean escape factor approximation. The results of the model obtained using atomic coefficients generated by the HULLAC atomic code are compared with experimental spectra emitted from laser-produced plasmas of highly charged xenon, barium, and cerium, and are used for interpreting the observed spectra, as well as for electron temperature and density estimates.