Vibrational excitation of ethane by electron impact

Differential cross sections for electron impact vibrational excitation of ethane (C 2 H 6 ) have been determined for incident energies from 3 to 20 eV over a scattering angular range of 20' to 130'. In addition, vibrational excitation functions were determined for impact energies of 2 to 15 eV at scattering angles of 30', 60', 90' and 120'. These measurements confirm the broad shape resonance at 7.5 eV but provide no evidence for a (second) resonance near 2.3 eV. A decomposition of the vibrational energy-loss spectrum shows strong resonance enhancement of selected vibrational modes, which may be explained by decay of a temporary negative ion (TNI) of symmetry species e u . A continuum multiple scattering calculation (CMS) reproduces these experimental results fairly well and indicates the simultaneous involvement of a TNI of species a 2u .