Beam-foil study of the Bowen system in neon V

The Bowen fluorescence mechanism was investigated by beam-foil spectroscopy because of the incompatible evaluations given by theory and experiment concerning its importance in exciting certain permitted oxygen lines in planetary nebulae. Since this excitation mechanism has already been studied by the beam-foil method of 0 III in detail, the present investigation examines the analogous transitions in other members of the isoelectronic sequence of carbon. In this manner, the disagreeing values for 0 III given by theory and experiment can be compared taking advantage of well-known quantum mechanical systematic trends along isoelectronic sequences. Specifically, the transitions in Ne V that correspond to the Bowen lines in 0 III were studied. For this purpose the optical spectrum of beam-foil excited 2.5 MeV neon was measured between lambda1700 A and lambda2400 A. From the subsequent measurements, the systematic behavior of the oscillator strength for the two-electron transition 2s2p33P0 - 2p3p 3S was established for the carbon sequence. The graphic display of this trend confirms that the previous experimental f-value for 0 III are more consistent with the other members of the isoelectronic sequence than the ones given by theory. Consequently, we support the conclusion of the previous experimental investigators. The Bowen fluorescence mechanism by itself is sufficiently strong to explain the observed intense 0 III lines in planetary nebulae. (orig.)