Theoretical study of the electronic spectra ofcis-1,3,5-hexatriene andcis-1,3-butadiene

Abstract

The electronic spectra forcis-1,3-butadiene andcis-1,3,5-hexatriene have been studied using multiconfiguration second-order perturbation theory (CASPT2) and extended ANO basis sets. The calculations comprise all singlet valence excited states below 8.0 eV, the first 3s, 3p, 3d Rydberg states, and the second 3s state. The four lowest triplet states were also studied. The resulting excitation energies forcis-hexatriene have been used in an assignment of the experimental spectrum, leading to a maximum deviation of 0.13 eV for the vertical transition energies. The calculations place the 11B2 state 0.04 eV below the 21A1 state. 16 excited states were studied incis-butadiene, using a CASPT2 optimized ground state geometry. The 11B2 state was located at 5.58 eV, 0.46 eV below the 21A1 state and 0.09 eV above the experimental value. No experimental assignments are available for the 15 other transitions.