PHOTOELECTRON-SPECTRA OF ETHYLENE AND OF THE 6 DEUTERATED DERIVATIVES

The photoelectron spectra of C2H4 and of six deuterated molecules of ethylene - C2D4, C2D3H, C2H3D, cis-C2H2D2, trans-C2H2D2 and gem-C2H2D2 - have been recorded with the 584-Å resonance line of He. The adiabatic ionization potentials of the X2B3u and the 2B3g states of the seven isotopic components have been determined with an accuracy of about 7 meV. The ionization potentials of the other excited electronic states have been measured with a lower accuracy owing to a less well defined onset. The measured ionization potentials of C2H4 are 10.514 eV, 12.431 eV, 14.43 eV, 15.74 eV and 18.7 eV. The vibrational structure of the first electronic band shows that the two normal modes ν2 (symmetric CC stretching) and ν3 (symmetric HCH bending) are excited simultaneously. The measured vibrational frequencies show no abnormal isotopic effect if the assignment given in the literature for the ν2 and ν3 modes in C2H4+ are reversed and if a stronger excitation of the ν3 symmetric bending mode in the least deuterated compounds is assumed. The vibrational modes most strongly excited in the second and third electronic bands are ν1 (symmetric CH stretching) and ν3, and in the fourth band ν3. © 1979.