Resonance Raman and density functional study of the A-band absorption of C5H5[WCCPh]O2

Resonance Raman spectra including absolute Raman cross-section measurements and density functional theory (DFT) calculations were performed to study the A-band absorption of C5H5[WCCPh]O2. The three most intense Franck–Condon active modes, the nominal WO stretch, CC stretch and CC stretch, show noticeable intensity in their overtones as well as their combination bands with each other. This is consistent with the changes in the HOMO–LUMO electron densities obtained from the DFT calculations. This suggests that the excited-state experiences significant structural changes simultaneously in the WO, CC and CC groups and the charge transfer is delocalized in the electronic transition.