The excited electronic states of all-trans-1,3,5-hexatriene

Extensive configuration interaction calculations based on ab initio wavefunctions including diffuse basis functions are reported for all-trans-1,3,5-hexatriene. Using these results we have assigned the one-photon spectra of Gavin and Rice and the electron-impact spectra of Kuppermann, and we have confirmed the assignment of the two-photon spectra of El-Sayed. The valence 2 ¹A_g state is found to lie above the strongly allowed valence 1 ¹B_u state.