Spectroscopy deals with the interaction of electromagnetic radiation with matter resulting in absorption or emission or scattering or reflection in discrete quanta. Spectroscopy is considered to be a powerful tool for the study of atomic, molecular, ionic, crystal structure and the results are applied to almost all branches of science. This book analyses the spectral characterization, probable assignments are suggested to the vibrational frequencies recorded in their spectra, factor group analysis, electronic state vibrations are obtained from the three complex flavone esters.