Fragmentation studies of CF$^+$ and HF$^+$ ions in collisions with cold electrons

The fundamental molecules composed of atoms from the second row of the periodic table (C,N,O,F) have a rich structure of excited potential curves that can be probed at high energy resolution by observing fragmentation processes following collisions with quasi-monochromatic electrons. Experiments of this type are performed in merged electron and ion beams at the ion storage ring TSR in Heidelberg, Germany. Using a cold, photocathode-produced electron beam, experiments on the system CF$^+$ yield rich structure in the collision energy dependence of both dissociative recombination (DR) and excitation (DE). The fragment-imaging technique shows a strong collision energy dependence of final ground and excited states of DR products. Moreover, an angular anisotropy of DR is observed for elevated collision energies. DR of HF$^+$ displays extremely low kinetic energy release of neutral fragments yielding resolution on initial rotational states of the ions. This predestines HF$^+$ to be used as ``molecular thermometer.''