The 2Ag− energy of crystalline all-trans-spheroidene as determined by resonance-Raman excitation profiles

The resonance-Raman excitation profiles of the CC and the C–C stretching Raman lines of crystalline all-trans-spheroidene were recorded at liquid-nitrogen temperature in order to determine the energy of the `optically-forbiddenʹ 2Ag− state. The CC stretching Raman line showed three distinct peaks at 14200, 15700 and 17250 cm−1, whereas the C–C stretching Raman line showed two clear peaks at 14200 and 15400 cm−1; therefore, the 0–0 origin of the 2Ag− state was determined to be 14200 cm−1. No additional peaks were found on the lower-energy side.