The diagnostic ratio of the intercombination and resonance lines of He-like ions: Influence of energetic electrons and non-stationarity
A new explanation of the anomalous high ratio of the He-like intercombination ( Y = 1s 2-1s2p 3P 1) and resonance ( W = 1s 2-1s2p 1P 1) lines is proposed which essentially differs from the known mechanisms like inner shell ionization from the Li-like 1s 22p levels and recombination from the H-like ions. The proposed mechanism is based on relaxation effects of allowed and forbidden components of the 1s2 l levels in fast heated or cooled plasmas. It explains rations that are higher than the ratio of the statistical weights of the triplet and singlet 1s2 l levels in hot transient regimes (where other methods fail) because it does not demand the presence of different ions beside the He-like ones. Low ratios can be entirely caused by relaxation effects in the heating phase and/or energetic electrons rather than by high electron density.