ROTATIONAL-EXCITATION OF DIATOMIC-MOLECULES AT INTERMEDIATE ENERGIES - ABSOLUTE DIFFERENTIAL STATE-TO-STATE TRANSITION CROSS-SECTIONS FOR ELECTRON-SCATTERING FROM N-2, CL-2, CO AND HCL

Absolute differential cross sections for the electron-impact rotational excitation of N-2, Cl-2, CO and HCl have been measured in a crossed-beam experiment. Results on rotational state-to-state transitions are obtained by a deconvolution procedure from the energy-loss peaks at primary energies between 10 eV and 200 eV and in the angular range from 10 degrees to 160 degrees. Details are given of an apparatus which allows absolute measurements with high-energy resolution and excellent statistics. At intermediate impact energies and scattering angles, unexpected large angular-momentum transfer was found. The results are very different for various energies and for different molecules. Four excitation mechanisms can clearly be distinguished. The experimental findings are compared with theoretical results using the semiclassical spectator model and a close-coupling calculation with an effective interaction potential.