THEORETICAL-STUDY OF THE ELECTRONIC-SPECTRA OF CIS-1,3,5-HEXATRIENE AND CIS-1,3-BUTADIENE

The electronic spectra for cis-1,3-butadiene and cis-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 for cis-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 1(1)B(2) state 0.04 eV below the 2(1)A(1) state. 16 excited states were studied in cis-butadiene, using a CASPT2 optimized ground state geometry. The 1(1)B(2) State was located at 5.58 eV, 0.46 eV below the 2(1)A(1) state and 0.09 eV above the experimental value. No experimental assignments are available for the 15 other transitions.