X-ray signatures of charge transfer reactions involving cold, very highly charged ions

Charge transfer reactions involving highly charged ions up to U91+ are bein g studied using x-ray spectroscopic techniques. The measurements are perfor med using ions produced in situ in a cylindrical trap with very low kinetic energy (less than or equal to 3 eV/amu). The observed K-shell and L-shell x-ray emission show prominent features from high-n levels decaying to the g round level. Such emission can serve as a diagnostic marker for charge tran sfer processes in plasmas, for example in cometary comae or in ion traps. T he emission is enabled by electron capture into states with low orbital ang ular momentum, mainly l = 1. The observed spectra, thus, provide a handle o n determining the fraction of electron capture into low-l states that can b e used for testing theoretical model in the limit of low collision energy. The present paper summarizes the progress made to date.