Abstract
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.