Photons shedding light upon basic charge exchange processes

Here we present recent progress made in our Photon Emission Spectroscopy studies of state selective electron capture in fundamental collision systems, like highly charged ions colliding on H.

In hydrogenic ions the l states are degenerate and therefore light emission from different l levels can not be resolved spectroscopically. However we succeeded to determine He+(4l) electron capture cross sections from the HeII(n = 4 --> n = 3) line emission by exploiting the relatively long and different lifetimes of the HeII(4l) states.

A further recent progress has been the extension of the experiments down to energies well below 1 keV/amu. Results for C4+ - H collisions will be presented and discussed on basis of the classical overbarrier model.

Finally we discuss the m state distribution of capture into C3+(3p) in collisions on molecular hydrogen. The distribution is deduced from the angular dependence of the related vuv radiation.