RESONANCE RAMAN SPECTRUM OF THE EXCITED 21A_g STATE OF ß‐CAROTENE

Abstract

Abstract— Resonance Raman (RR) bands assignable to the 2 1 A g excited state of ß‐carotene are recorded using picosecond time‐resolved resonance Raman (PTR 3 ) spectroscopy. The RR spectrum contains bands in both the C‐C (1204 cm −1 , 1243 cm −1 , and 1282 cm −1 ) and C=C (1777 cm −1 ) stretching regions. The time‐dependent intensities of these RR features, measured with ˜ 30 ps. resolution, are found (i) to closely correlate with picosecond transient absorption (PTA) data recorded at 575 nm on the same sample and (ii) inversely correlate with the time‐dependent intensities of RR bands assigned to the 1 1 A g ground state. Both of these observations support the assignment of these four RR features to the 2 1 A g excited state. These results remove uncertainties associated with earlier experiments in which excited‐state RR scattering from (3‐carotene was not observed in spite of predicted trends emanating from studies of shorter polyene compounds. The observed C=C band position also agrees with a recent report of this feature.