Detailed experimental studies of the profile of the ${\mathrm{H}}_{\alpha }$ line emitted by hydrogen atoms in dense helium plasmas revealed a structure on the blue wing. It appears as a dip and was observable only for special plasma conditions. The position did not vary with the electron density, which was determined independently by Thomson scattering. It is suggested that the feature is caused by the crossing of terms of a two-center quantum system consisting of the radiating hydrogen atom and a perturbing fully ionized atom of different nuclear charge.

• Received 19 December 1994

DOI:https://doi.org/10.1103/PhysRevLett.75.4740