Since decades, intercombination transitions and dielectronic satellite emission have played an important role for plasma spectroscopy [1, 2]. The present overview is devoted to the particular importance of these atomic data for the description of the radiative properties of non-equilibrium and optically thick plasmas. We will show, that their relative importance strongly depends on the plasma conditions, in particular opacity effects and particle diffusion turned out to be very important. The effects are discussed together with examples from high density and low density plasmas. The first example concerns the neutral helium emission in the plasma edge in magnetic fusion. Here, the relevance of intercombination transitions strongly depends on the equilibrium conditions: in diffusive plasmas the radiation emission originating from the singlet and triplet levels is markedly influenced (order of magnitude) whereas under equilibrium conditions, the inclusion of intercombination transitions leads only to small corrections. The second example is devoted to the dielectronic satellite emission in high density plasmas. For large resonance line opacity, the temperature diagnostic based on the dielectronic satellite emission is seriously perturbed. We show, that usually neglected higher order satellite transitions will be able to replace the resonance line as a reference line. The comparison of atomic data calculated with different methods show, that the agreement is very good for n=2 satellite transitions, however, for higher order satellite transitions (spectator electrons in n = 3, 4, 5 quantum shell) important discrepancies show up. It is therefore concluded, that the importance of certain atomic data cannot simply be estimated from equilibrium calculations. Non-equilibrium and opacity effects may lead to entirely different aspects and have therefore carefully be considered for the relevance of atomic data.

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