He I and He II photoelectron spectra of isomeric nitropropenes

The He II photoelectron spectra of 1-, 2- and 3-nitropropene have been recorded and compared with the corresponding He I spectra. The variation in relative He I/He II band intensities allows unequivocal classification of bands into those associated with orbitals of the nitro group and those with orbitals of the hydrocarbon moiety. Band assignment is also aided by observed vibrational structure, band shape and SCF MO calculations. The variation of the relative energies of the orbitals πCC, n+0, n–0 and π2 among the isomers is discussed in terms of inductive, hyperconjugation and resonance effects.