Rate enhancement in the recombination ofBi80+ions with electrons

Abstract

Recombination of ${\mathrm{Bi}}^{80+}$ ions with electrons at low relative energies has been investigated employing the electron cooler at the experimental storage ring of the Gesellschaft f\ur Schwerionenforschung in Darmstadt. Absolute recombination rate coefficients have been determined for relative energies ${E}_{\mathrm{rel}}$ between $1\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}5}$ and 10 eV. Simulations of cooling-force effects were carried out to assure the validity of these energies. In the range 10 meV $\ensuremath{\lesssim}{E}_{\mathrm{rel}}\ensuremath{\lesssim}10\mathrm{eV}$ the measured rate coefficients agree well with the theory for radiative recombination (RR). Towards lower relative energies ${(E}_{\mathrm{rel}}\ensuremath{\lesssim}10\mathrm{meV})$ the measured rate coefficients increasingly exceed the prediction of the RR theory. At the lowest accessible relative energy the ratio of measured and calculated rates reaches a factor of 3.5. The enhancement is found insensitive to a variation of the electron density from $1.6\ifmmode\times\else\texttimes\fi{}{10}^{6}$ to $4.8\ifmmode\times\else\texttimes\fi{}{10}^{6}{\mathrm{cm}}^{\ensuremath{-}3}.$