Spectroscopic signatures of avoided crossings caused by charge exchange inplasmas

Electron terms in the field of two stationary Coulomb centres (TCCs) of cha rges Z and Z' separated by a distance R are a fundamental problem of quantu m mechanics, presenting fascinating atomic physics: the terms show crossing s and avoided crossings. In the latter situation, the electron has a much l arger probability of tunnelling from one well to the other (i.e. of charge exchange) than in the absence of such degeneracy. These rich features of th e TCC problem are also manifest in different areas of physics such as plasm a spectroscopy. Recently it was shown experimentally that charge exchange, enhanced by the encounter of two TCC terms, can result in an unusual struct ure (a dip) in the spectral line profile emitted by a Z ion from a plasma c onsisting of both Z and Z' ions. In this paper we present a detailed quanti tative theory of this phenomenon, in which its origin is directly traced to the avoided crossings of terms in the TCC problem. We show that our theory explains quantitatively all the results of the above experiment where such a dip was observed in a hydrogen line. We also consider in detail several prospective 'radiator-perturber' pairs for observing these signatures of ch arge exchange in lines of hydrogen-like ions. Further experimental studies of such dips would serve to produce not-yet-available fundamental data on c harge exchange between multicharged ions, virtually inaccessible by other e xperimental methods.