Interferences in the Raman excitation profile for the intensity of normal modes of aggregated chlorophyll a

Abstract

If dry chlorophyll a is dissolved in dry nonpolar solvents, aggregation takes place and the degree of aggregation depends on the con centration of this large molecule. The pulsed laser-induced Raman spectrum of such solutions contains contributions from many species, including scattering from excited states in case the laser wavelength is in resonance with the Soret band. At resonance, the Raman intensities experience changes but the presence of close-lying short-lived excited states causes sharp interferences. They occur over a range of 50 cm-1 in the Soret band having a width of ~500 cm-1. Such patterns are fingerprints for such complicated molecules. Temporal aspects due to excited state Raman scattering also influence these profiles. Besides results on chlorophyll a in solution, we also show such interferences for electronic Raman scattering and discuss differences between the electronic and vibrational scattering processes.