The electron impact spectra of some mono-olefinic hydrocarbonsa)

Electron impact spectra of ethylene, propylene, isobutene, trans-butene, cis-butene, trimethylethylene, and tetramethylethylene have been obtained at scattering angles of 0° and 90° and at impact energies from ?20 to 150 eV. The spectra scan an energy-loss region from 2.5–15 eV. All of the observed Rydberg transitions of the methyl derivatives are correlated to corresponding Rydberg transitions of ethylene. The missing π→3p transitions of ethylene are tentatively located via this correlation. Evidence is also presented for assigning the N→3R′ system of ethylene (at 8.26 eV) to a π→3px transition. Possible assignments of some broad continua above ?8–9eV as σ→π* and σ→σ* transitions are considered. In agreement with other reported large-angle electron impact spectra, no evidence is obtained for transitions that could be assigned to triplet Rydberg states. However the π→π* triplet transitions are all clearly located with transition energies in good agreement with those obtained by a variety of other techniques.