The Raman excitation profile spectrum of β-carotene in the preresonance region: Evidence for a low-lying singlet state

The Raman excitation profile spectrum of the ν1 band of trans-β-carotene has been obtained in the preresonance region (16 900–19 000 cm−1). Five features are found in the spectrum which are interpreted as vibrational structure of a low-lying excited 1Ag state with its origin near 17 230±100 cm−1. This corresponds to a 1Bu−1Ag energy gap of 3470±100 cm−1, and may help account for the nonfluorescence of β-carotene.