In spheroidene (having the number of conjugated double bonds n = 10), stimulated emission was observed from the mixed vibronic levels of 1B(u)(+)(0) + 1B(u)(-)(2) and 1B(u)(-)(1) + 1B(u)(-)(3), whereas in lycopene, anhydrorhodovibrin and spirilloxanthin (n = 11-13), stimulated emission, from the pure vibronic levels of 1B(u)(+) (0) and 1B(u)(+)(1). Thus, the 1B(u)(+) state can mix with the 1B(u)(-) state but not with the 3A(g)(-) state, both being located just below the 1B(u)(+) state. The presence and absence of the mixing of the neighboring diabatic states support the symmetries of the next low-lying 1B(u)(-) and 3A(g)(-) states. (c) 2007 Elsevier B.V. All rights reserved.