Photoionization of O III low-lying states: autoionization resonance energies and widths of some 1s-2p excited states

Twenty-four-state close-coupling calculations are performed on the inner-shell photoionization of the terms belonging to the configurations 2s 2 2p 2 and 2s2p 3 of the O III ion. The resonance energies and widths of the transitions of a 1s electron excited into the 2p orbital are determined by analysing the resonance structures of the photoionization cross sections. The calculations show that the autoionization resonance widths of these inner-shell transitions are larger than the corresponding Doppler full width at half maximum (FWHM) and Stark FWHM by a factor of two or three under typical plasma conditions (such as a temperature of 10 eV and a density of 0.0016 g cm -3 ). The autoionization resonance broadening is obviously the main broadening mechanism and should be considered when analysing the plasma spectrum. Only when the electron density is larger than 5×10 21 cm -3 may the Stark FWHM be larger than the autoionization resonance FWHM.