EXCITED-STATE GEOMETRIES DERIVED FROM THE ANALYSIS OF RESONANCE RAMAN-SPECTRA - EXAMPLE - (1)(PI-PI-ASTERISK) STATE OF 3,5-DI-TERT-BUTYL-O-BENZOQUINONE

Resonance Raman spectra of 3,5-di-tert-butyl-o-benzoquinone were obtai ned by exciting its lowest (1)(pi-pi) state. The resonance enhancemen t of two stretching modes (C=C, C=O) and of one C-H bending mode was a nalyzed applying the Kramers-Heisenberg-Dirac relation. The mathematic al fitting of the experimentally derived spectra yielded the magnitude of the Dushinsky mode mixing and the displacements of the potential c urves along the considered normal modes. These displacements were tran sformed to bond-length changes with the use of the eigenvector matrix L of the ground-state vibrations. The excited-state geometry is charac terized by the unsymmetric lengthening of the C=C bonds within the acr olein subunits and a shortening of the C-C bond inside the butadiene s ubsystem.