Shifts of ionized-helium lines from electron collisions in dense plasmas

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Abstract
The semiclassical impact-parameter method is used to calculate shifts of ionized helium lines in the first three spectral series caused by electrons in a plasma. These shifts together with opposite and smaller shifts due to ion quadrupole interactions are in agreement with observed shifts of lines corresponding to the Paschen series of hydrogen. Adding plasma polarization shifts according to the linearized Debye model to the shifts calculated here results in overestimates by a factor of 2 for the shifts of these lines. For lines corresponding to the Balmer series such addition may be consistent with measurements, while for the Lyman series all present theoretical models are found inadequate.