Abstract
A theoretical model is constructed to describe the influence of selective radiative pressure on the concentration distribution of metals in the lower chromosphere. The limit of weak collisional coupling is considered. It is shown that radiative pressure leads to non monotonic concentration profiles of metals (Mg, Ca, Na, Fe) with pronounced element separation with height, as well as to non monotonic profiles of electron concentration and total pressure. It is shown that the absorption spectrum of the negative hydrogen ion and the ambipolar diffusion of metal ions partially smooth the peak concentrations but do not eliminate the separation completely.