No theoretical and experimental information has been available for the role of each atom in infrared (IR) and Raman spectra of polyene derivative systems. Analyzing atomic polar and polarizability tensors at each carbon site in the C=C bond fixed frame, we find that in IR intensities, the motions of carbon atoms in the proximity of a substituent are important, while in Raman intensities the carbon motions in the central region are important. The strong IR and Raman intensities appear for the concurrent C=C stretch/contraction motion in nonsymmetric polyenes. (C) 1997 American Institute of Physics.