Method for determining absolute partial cross sections for radiative and nonradiative deexcitation of metastable hydrogenlike ions

Abstract

In this work we present a method developed to measure separately the radiative and nonradiative contributions to the cross section for collisional deexcitation of metastable hydrogenlike ions. We present the results of the first experiment applying this method, where deexcitation of metastable ${\mathrm{He}}^{+}(2s)$ ions in collisions with argon atoms is considered. First the total deexcitation cross section for 6.6 keV ${}^{4}{\mathrm{He}}^{+}(2s)$ ions is measured absolutely in a beam-gas attenuation experiment. Then the absolute cross section for nonradiative deexcitation is measured separately by coincident detection of projectiles keeping their initial charge state 1+ and recoil ions (formed only in nonradiative deexcitation events). Further, we discuss a semiclassical calculation of the radiative deexcitation cross section, in which the influence of competing electron-capture processes is taken into account in a semiempirical fashion. The result is in agreement with the measured radiative deexcitation cross section of $(5.4\ifmmode\pm\else\textpm\fi{}1.3)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16} {\mathrm{cm}}^{2},$ which amounts to $(70\ifmmode\pm\else\textpm\fi{}8)%$ of the total deexcitation cross section.