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 t heory (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 state s were also studied. The resulting excitation energies for cis-hexatri ene have been used in an assignment of the experimental spectrum, lead ing to a maximum deviation of 0.13 eV for the vertical transition ener gies. 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 C ASPT2 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 exp erimental value. No experimental assignments are available for the 15 other transitions.