Polarization propagator study of electronic excitation in key heterocyclic molecules II. Furan Original Research Article

The electronic spectrum of furan is investigated theoretically beyond the previous vertical-electronic description. A polarization propagator method referred to as second-order algebraic-diagrammatic construction (ADC(2)) has been used in the electronic structure calculations. The vibrational excitation accompanying the electronic transitions is described with the aid of a linear electron-vibrational coupling model. The spectral information thereby obtained permits extensive comparison with experiment. The average accuracy of the present method, estimated by comparing adiabatic transition energies, is better than 0.4 eV. Only for the lowest π-π∗ valance transition, V′(1A1) and V′(1B2), and for the Rydberg excitations agree The results for the other π-π∗ valence transitions, V(1B2), and for the Rydberg excitations agree well with findings of previous experimental and theoretical work. A (multistate) vibronic coupling effect involving the V′(1A1) and V(1B2) valence transitions and the 3s(1A2 Rydberg excitation is suggested as the reason for the highly diffuse character of the 5.7–6.7 eV photoabsorption band.