BA+ RESONANCE-LINE EXCITATION IN PLASMAS

The rate of excitation by electron collisions of the 6P2 levels of the Ba+ ion is experimentally determined as a function of electron temperature in the range 2500-6000K. The measured rate is the sum of the excitation rates from the 6S2 ground state and from the metastable 5D2 states. The rate coefficients, as well as the corresponding electron temperatures, are obtained from population densities of the 6P2, 6S2, and 5D2 levels. The 6S2 and 5D2 population densities are determined from resonance fluorescence measurements and the 6P2 densities from the emitted light intensities. Approximate near-threshold excitation cross sections are deduced from the rate coefficients. Either the absolute rate coefficients or the ratio of excitation rates to the two 6P2 levels is suitable for electron thermometry in low-density plasmas where photoexcitation and radiation trapping are negligible. © 1969 The American Physical Society.