Electron capture to Rydberg states: C⁴⁺in collisions with H₂

Abstract

The problem of extracting selective information on the distribution of final-state (nl) population following high-energy electron capture is addressed. As a prototype reaction, the authors study the quasihydrogenic system C4+(1s2)+T going to C3+(1s2nl)+T(?) at energies 2<or=E<or=5 MeV, where T=H2 or He. Theoretically, two multiple scattering approaches (IA and CDW) are generalised to include capture to high-lying states (nl arbitrary), and experimentally the EUV emission spectra subsequent to the capture process are examined. The experimentally deduced cross sections for final states 3<or=n<or=10 and l=0, 1, 2 are then compared with theory. The data satisfy the n-3 law and the experimental trends are equally well reproduced by the IA or CDW calculations. In contrast, the first and second Born cross sections are found to be inadequate to represent the data. This in turn gives further evidence of the inadequacy of the latter theories and provides a measure of the importance of multiple scattering effects in capture processes. To the authors' knowledge, these results represent the first quantitative comparison between theory and experiment in this high-energy regime and at this level of discrimination.