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We have studied the resonance Raman spectra of β-carotene in solution and in protein-complexes using laser excitation at various wavelengths in the visible region. Main focus was laid on the v 1 -band, which shows an anomalous behaviour upon variation of the excitation wavelength resulting in a frequency shift of the peak maximum. This shift is due to different excitation profiles of two closely spaced modes as shown previously for β-carotene in solution. In this work, we have extended the studies to the antenna pigment in photosystems I and II (PS I and PS II).

In the present work we have studied β-carotene dissolved in dichloromethane by means of resonance Raman spectroscopy. To obtain the Raman excitation profiles Raman spectra of /3-carotene have been acquired at various wavelengths throughout the visible region. It was found that the position of the prominent peak at ca. 1524 cm -1 varies with the excitation wavelength indicating the involvement of two different modes. Possible origins of the different enhancement pattern of the two modes are discussed.