Rotational excitation of N₂, CO and H₂O by low-energy electron collisions

Absolute total and differential rotational and rotational-vibrational cross sections have been measured for N₂ (weak quadrupole), CO (weak dipole), and H₂O (strong dipole). In the beam experiments, the range of collision energies of the electrons was chosen between 0.5 and 6 eV, and the range of scattering angles from 15 to 105 degrees was covered. The overall energy inhomogeneity of the electron spectrometer was between 10 and 18 meV FWHM, depending on the experiment. Direct and resonant rotational excitation has been measured. In the case of N₂ the rotational branches with Delta J=0, +or-2, +or-4 have been fitted to energy-loss spectra and for each branch a cross section is given. The authors have proceeded similarly in the case of CO (for dipole excitation Delta J=0, +or-1, for excitation via the ² Pi resonance Delta J=0, +or-1, ..., +or-4) and in the case of H₂O ( Delta J=0, +or-1). For N₂ and CO the results are compared with calculated angular dependences. Finally, the cross sections are listed according to the different types of interaction potentials and interaction mechanisms.