Theoretical study of the π → π * excited states of linear polyene radical cations and dications

Multireference Møller-Plesset theory is applied to the study of the valence π → π * excited states of radical cations and dications of butadiene, hexatriene, octatetraene and decapentaene. The present theory satisfactorily describes the low-lying excited states of cations within an error of 0.1 eV. Theory confirms the general tendency observed in carotenoids that the first transition of the dications of polyenes is at a higher energy than the intense transition of the radical cations and at a lower energy than the first allowed transition of the neutral species.