Systematic red shifts for the Paschen α, β, and γ lines (n=4,5,6→n=3) of He II are observed over an electron density range of (1-8)×{}10²² m^-3. The measurements are compared with combined estimates for plasma polarization and ion quadrupole effects. It is demonstrated that previous theoretical estimates have left out an important contribution to the polarization shift, which we estimate using the Debye model.
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Pittman et al. (1980) studied this question.