Two-photon excitation spectroscopy of a substituted all-trans hexatriene (iso-tachysterol). Spectroscopic assignments of the low-lying 1‘‘1B u*+’’ and 2‘‘1A g*−’’ ππ* states

The two-photon excitation spectrum of the substituted all-trans hexatriene, iso-tachysterol, is taken in EPA (77 K). Comparison of this spectrum with the one-photon absorption and fluorescence spectra indicate that the system origin of the 2’’ 1A*−’’g state lies slightly below the 1’’ 1B*+’’u system origin in EPA (77 K). (AIP)