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.