| Abstract
| - Hyper-Raman scattering of all-trans-retinal was measured for the first time in solution at room temperature.Under the two-photon resonance condition, the intensity of hyper-Raman scattering was so strong that itcould be measured from a diluted solution at a concentration as low as 1 × 10-3 mol dm-3. Hyper-Ramanexcitation profiles were examined in the excitation wavelength range from 770 to 840 nm (λex/2, 385−420nm). In this excitation range, the intensity of all the hyper-Raman bands monotonically increased with shorteningexcitation wavelength, and the hyper-Raman spectral feature was very similar to that of resonance Ramanspectra excited with double the excitation energy (λex/2). The resonance mechanism of hyper-Raman scatteringwas discussed, and it was concluded that hyper-Raman scattering gains intensity enhancement from a two-photon resonance with the “Bu*” state, not with the “1Ag*” state, through the Franck−Condon (the A term)mechanism.
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