Near-threshold electron impact rovibrational excitation of HCl and HF

Differential cross sections for the electron impact rovibrational excitation of the hydrogen halides HCl and HF have been measured in absolute units in the primary energy range from 0.15 eV up to several eV and in the angular range from 15' to 135'. Simultaneous to the excitation of the first vibrational level strong rotational transitions have been observed in the threshold peaks of the excitation functions. In addition the angular dependences close to threshold are found to be non-isotropic. These results indicate the importance of contributions from higher partial waves and the occurrence of strong nonadiabatic coupling effects at the vibrational thresholds. The theoretical approaches developed so far are discussed and compared with the present experimental results.