Abstract
Energetic 0.55-2 keV photons produce efficiently 1s-hole and 1s+2p-hole oxygen ions by single ionization and shake off processes of neutral oxygen, respectively. This last effect is estimated to exceed 25 percent of the single one, reaching its full efficiency at above 0.8 keV. Auger decays of these 1s-hole ions will produce O III and O IV excited states giving rise to O III and O IV ultraviolet and optical lines. In low density plasmas submitted to a source of energetic photons with soft X-ray excess below 1 keV this direct production of excited states must be taken into account before using [O III] and O III] lines as indicators of Te or Ne since λλ4960, 5008, λλ1661, 1667 are indirectly affected by Auger decay. Auger and radiative rates for O IV residual ion are presented in a convenient form for evaluating effective Auger rates and relative intensities for O III and O IV lines produced by low density plasmas under soft X irradiation.
