Cross sections for resonant transfer and excitation in Feq++H2 collisions.

Abstract

Resonant transfer and excitation (RTE) is investigated for Fe{sup {ital q}+} ions ({ital q}=23, 24, and 25) colliding with H{sub 2}. For each charge state, cross sections for RTE were obtained from measurements of {ital K} x rays, emitted from the doubly excited intermediate state, coincident with single-electron capture by the incident ion. Additionally, for Fe{sup 25+} cross sections were obtained from measurements of coincidences between the two {ital K} x rays emitted from the intermediate state. These latter measurements provide information on the lifetimes of intermediate metastable states formed in the RTE process. In all cases, measured cross sections are in good agreement with calculations based on theoretical cross sections for dielectronic recombination (DR). Since RTE closely approximates DR, the results indicate that dielectronic-recombination cross sections involving {ital K}-shell excitation can be accurately predicted for highly charged iron ions. The results for Fe{sup 25+} show that metastable states are sufficiently short lived to be observable in the RTE (or DR) process for these hydrogenlike ions.