Excitation followed by stimulated-emission from diabatic levels in all-trans- and 15-cis-β-carotenes: Effects of molecular symmetry and solvent polarity

β-Carotene exhibits the 1Bu+→3Ag- diabatic excitation followed by stimulated-emission from the 3Ag- and 1Bu- states when the C2h symmetry of electronic structure is lowered by polarization.