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Absolute differential cross sections for the electron impact rovibrational excitation of the upsilon =2 and upsilon =3 levels of HF and HCl have been measured in the energy range from threshold up to several eV in the angular range 15-135 degrees . Threshold peaks are found which show strong rotational excitation with non-isotropic angular distributions. In the upsilon =3 excitation function of HF a resonance structure occurs below the cusp of the opening of the upsilon =4 channel. This is the first experimental proof of the existence of nuclear-excited Feshbach resonances. In the case of HCl the threshold peak in the upsilon =3 excitation functions indicates the existence of a second non-dissociating negative-ion state at low energies.

Differential cross sections for the electron impact excitation of HCl and HF have been measured in a crossed-beam experiment. Results on rotational and rovibrational state-to-state transitions are obtained by a deconvolution procedure of the energy loss peaks at primary energies between 0.5 and 10 eV and in the angular range from 15 to 135'. In the case of HCl the angular dependences and the excitation functions demonstrate the interplay of direct and resonant interactions. For HF only direct interaction has been observed. The results are compared with different theories.

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.