Vacuum ultraviolet resonance Raman studies of the excited electronic states of ethylene

A resonance Raman study of ethylene has been performed with the use of excitation wavelengths ranging from 200 to 141 nm. Excitation resonant with the V(ππ*) state results in Raman spectra exhibiting intensity in the C=C stretching vibration, the CH₂ symmetric scissors vibration, the CH₂ torsional vibration and the CH₂ out-of-plane wagging vibrations. These spectra confirm that the V state is strongly twisted about the C-C bond. They also indicate that the C=CH₂ groups are no longer planar in the V state. Resonance with the (π3s) and (π3p) Rydberg transitions results in spectra exhibiting much less intensity in the torsional vibration, the CH₂ symmetric scissors vibration and the CH ₂ wagging vibrations. The spectrum obtained in resonance with the (π3d) Rydberg transitions once again exhibits activity in the CH₂ symmetric scissors mode.