L-shell resonant transfer and excitation in niobium ions.

Abstract

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