EXCITED-STATES IN POLYENE RADICAL CATIONS - AN AB-INITIO THEORETICAL-STUDY

The lowest pi- and sigma-doublet excited states of butadiene, hexatrie ne and octatetraene radical cation are studied using multiconfiguratio nal second-order perturbation theory. The calculated excitation energi es are found to be within less-than-or-equal-to 0.2 eV of the experime ntal energies. Our results allow us to interpret the different feature s observed in photoelectron spectra which are measured at the ground s tate geometry of the neutral molecules as compared to the electronic a bsorption spectra which are taken at the ground state geometry of the cations.