Shifts of hydrogen and ionized-helium lines fromΔn=0interactions with electrons in dense plasmas

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Abstract
Shifts from electron collisions associated with dipole interactions between degenerate levels of a given principal quantum number n are evaluated following D. B. Boercker and C. A. Iglesias [Phys. Rev. A 30, 2771 (1984)]. They are then used to recalculate the plasma shifts of hydrogen and ionized-helium lines from electron collisions, inhomogeneities in the ion-produced quasistatic fields, and some higher-order effects. Because of the partial cancellation of electron collisional shifts by the other effects, inclusion of the Δn=0 collisional shifts leads to an increase of calculated line shifts by a factor ∼1.5, which for Balmer lines of hydrogen and Paschen lines of ionized helium leads to markedly improved agreement with most measurements. Estimates for higher-Z members (Z≥4) of the one-electron isoelectronic sequence yield Δn=0, dipole contributions to the electron-collisional shifts which are much smaller than the effects of Λ=0, penetrating monopole interactions.