Stimulated emission from the (0) level and the (0) + 1 (1 and 2) diabatic levels upon excitation to the 1(0) level in neurosporene and spheroidene

Excitation with ∼30 fs pulses to the 1 B u + (0) vibronic level of neurosporene and spheroidene (having n = 9 and 10 double bonds) in tetrahydrofuran generated a single persistent stimulated emission with the 1 B u + (0) energy as well as the 1 B u - (0) stimulated emission; the measured energies agreed nicely with those determined by measurement of resonance-Raman excitation profiles [K. Furuichi, T. Sashima, Y. Koyama, Chem. Phys. Lett. 356 (2002) 547]. The observation is ascribed to simultaneous coherent excitation to the optically-allowed 1 B u + (0) and isoenergetic optically-forbidden 1 B u - (1) or 1 B u - (2) levels (‘diabatic levels’) followed by rapid vibrational relaxation.