Vibrational relaxation on the mixed vibronic levels of the and states in all-trans-neurosporene as revealed by subpicosecond time-resolved, stimulated emission and transient absorption spectroscopy

In all-trans-neurosporene, whose 1 B u - ( 0 ) level is lower than the 1 B u + ( 0 ) level by one vibrational quantum, the following two steps of vibrational relaxation from the mixed vibronic states were identified, in the order, 1 B u + ( 1 ) + 1 B u - ( 2 ) stimulated emission → 1 B u + ( 0 ) + 1 B u - ( 1 ) stimulated emission → 1 B u - ( 0 ) transient absorption. The stimulated emission patterns were simulated by the use of Franck–Condon factors in the transitions from the pair of mixed vibronic levels down to the ground 1 A g - ( υ ″ ) vibronic levels. The vibronic levels of the mixed 1 B u + and 1 B u - state were characterized theoretically based on the diabatic approximation.