Deconvoluting the visible absorption spectrum of methyl orange using inverse Raman transform techniques

Abstract

Resonance Raman excitation profiles have been measured for all the active vibrations between 800 and 1600 cm−1 over the visible absorption band of methyl orange. The excitation profiles indicate that two transitions contribute to the observed absorption band profile, and that individual vibrations appear to be enhanced via resonance with single electronic transitions. Using inverse Raman transform techniques, the absorption bands responsible for the resonance Raman activity are determined from the excitation profiles of the 924 and 1393 cm−1 modes. Two distinct absorption bands with maxima at 437 and 475 nm are found to fit the excitation profiles and inverse transform results. The transitions responsible for these bands are determined from qualitative molecular orbital arguments and are assigned to nπ* and charge transfer excitations.