State selective electron capture in collisions of C6+ and O8+ on atomic and molecular hydrogen studied by photon emission spectroscopy

In the impact velocity range of 0.2-0.6 a.u. (1-9 keV/amu) we have measured absolute line emission cross sections in the VUV and visible spectral region for C6+ and O8+ colliding with H and H2. For charge transfer between bare carbon or oxygen ions and atomic hydrogen we find good agreement with theory regarding the dominant capture channels. However discrepancies are observed in the case of capture into non-dominantly populated states. For collisions on molecular hydrogen it is found that two electron capture with subsequent autoionization contributes significantly to the apparent one electron capture cross section. For collisions both with atomic and molecular hydrogen we make a detailed comparison with all other experimental results available from charge exchange, soft X-ray and electron spectroscopy measurements to check the consistency of the measurements. For the system C6+ + H2 a consistent set of cross sections for the various charge exchange processes is derived. (orig.)