SOFT X-IRRADIATION OF LOW-DENSITY PLASMAS - O-III AND O-IV LINE EMISSION

Energetic 0.55-2 keV photons produce efficiently 1s-hole and 1s+2p-hol e oxygen ions by single ionization and shake off processes of neutral oxygen, respectively. This last effect is estimated to exceed 25 perce nt of the single one, reaching its full efficiency at above 0.8 keV. A uger decays of these Is-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 s oft 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 in dicators of T-e or N-e since lambda lambda 4960, 5008, lambda lambda 1 661, 1667 are indirectly affected by Auger decay. Auger and radiative rates for O IV residual ion are presented in a convenient form for eva luating effective Auger rates and relative intensities for O III and O IV lines produced by low density plasmas under soft X irradiation.