Vibrational excitation in low-energy e–C₂H₆ scattering

In a crossed-beam experiment, vibrational excitation (VE) of ethane by electron impact has been measured for collision energies in the range E = 1– 10 eV. The energy resolution is 30 meV (FWHM) in the energy-loss mode. The observed VE processes are divided into three groups: (i) CH stretching modes with a mean energy loss of ΔE = 365 meV; (ii) CH₃ deformation modes with ΔE = 180 meV; (iii) CC carbon chain vibrations with ΔE = 125 meV. Absolute differential and integral cross sections are determined for the three groups of vibrations. The results are interpreted by two principal VE mechanisms: direct excitation for energies below 3 eV and resonant excitation for energies around 7–8 eV. At low energies (E < 3 eV) the present results are compared with the results from swarm experiments, while for E ≥ 3 eV the present measurements resolve some discrepancies between the results of two previous beam experiments. The present work complements a previous study by the same authors on elastic e–C₂H₆ scattering in this energy range.