Observation of resonance electronic and non-resonance-enhanced vibrational natural Raman optical activity

Natural resonance electronic Raman optical activity (ROA) is observed for the first time. Coincidently, the first example of vibrational ROA enhanced by low-lying electronic transition is reported. These new phenomena were measured using the rare-earth complex Eu(tfc)(3) (+)-tris[3-trifluoroacetyl-D-camphorato]europium(III), where electronic resonance occurs between the 532-nm laser excitation and the (7)F(1) -> (5)D(1) transition of the Eu(3+) metal center. Electronic Raman spectra involve the Raman transitions terminating on the low-lying electronic states of Eu(tfc)(3). The observed vibrational ROA spectra are enhanced relative to typical ROA spectra by the proximity of vibrational states of Eu(tfc)(3) to its low-lying electronic states with significant magnetic-dipole character, whereas the parent vibrational Raman spectra do not appear to be resonance-enhanced since the 532-nm vibrational Raman spectrum has similar relative intensities to the corresponding Raman spectrum measured with 1064-nm laser excitation. Copyright (C) 2010 John Wiley & Sons, Ltd.