K-shell resonant transfer and excitation in calcium ions.

Abstract

We have calculated {ital L}-shell cross sections for the process of resonant transfer excitation followed by x-ray stabilization (RTEX) in collisions of Nb{sup {ital q}+} ions ({ital q}=28--32) with H{sub 2}. The {ital LMn} plateau cross section is nearly constant ((4.5--5.2){times}10{sup {minus}20} cm{sup 2}) for {ital q}=29--32 and is consistent with the results of the recent experiment by Bernstein {ital et} {ital al}. (Phys. Rev. A 40, 4085 (1989)) for {ital q}=31 and 32, but our results for {ital q}=28--30 are substantially larger than experiment. For Ne-like niobium ({ital q}=31), the inclusion of RTEX contributions from higher transitions ({ital LNn}, {ital LOn}, etc.) leads to good agreement with the experiment by Bernstein {ital et} {ital al}. in the high-energy tail. This implies that only a small contribution is possible from the uncorrelated transfer excitation process.