Bowen Fluorescence, Stark Broadening, and Transition Probabilities in the O III Spectrum

The intensity ratios of the 344.405, 342.863, and 343.057 nm spectral lines of doubly ionized oxygen (O III), which originate from the 2p3d³P levels, have been investigated in optically thin laboratory plasmas in pure oxygen and helium-oxygen mixture at 42,000 and 47,000 K electron temperatures and at electron densities in the range 10²²-10²³ m^-3. Two of them (344.405 and 342.863 nm) belong to the primary cascade in the astrophysically important Bowen fluorescence mechanism. On the basis of the I(344.405 nm)/I(342.863 nm), I(344.405 nm)/I(343.057 nm), and I(343.057 nm)/I(322.863 nm) O III line intensity ratios, in pure oxygen and helium-oxygen plasmas, we have found that the 343.057 nm O III spectral line also shows fluorescence tendency caused by the Bowen mechanism not evident up to now. The transition probability values (Einstein's A-values) of these transitions are obtained by means of the relative line intensity ratio (RLIR) method using, for the first time, the O III spectral lines in emission spectra. We have found that our experimental transition probabilities agree well with calculated A data based on the multiconfiguration Hartree-Fock approximation (MCHF) including the Breit-Pauli potential. Besides, the A-values of the 342.736 and 344.036 nm lines, belonging to the forbidden 3s-4d O III transitions, are also obtained. They are the first measured data. Stark broadening parameters [line width (W) and shift (d)] of the mentioned O III lines have also been measured. They are the first published data.