Quadrupole Contributions to the Electron Broadening of Overlapping Neutral-Atom Lines in a Plasma

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Abstract
The impact-parameter formalism for Stark broadening of partially degenerate neutral lines emitted by an atom immersed in a dense plasma is extended to include the quadrupole term of the electron-atom interaction, considered in the second order of the Dyson expansion. The corresponding nondiagonal broadening functions and their impact-parameter averages are derived and their properties are studied in detail. The nondiagonal quadrupole shift function is shown to be negligible with respect to the dipole term, for most situations of physical interest. These new functions are also useful in the collision theory of electrons with atoms and molecules.