The dipole-induced dipole (DID) mechanism for generating Raman and optical Kerr effect (OK-E) intensities is extended to include the effect of the interaction between first hyperpolarizability and dipole field. This extended mechanism, called 'extended DID' (XDID) mechanism, is used to calculate Raman spectra and OKE signals of liquid formamide and N-methylformamide. It is shown that the effect of the newly added term in the XDID mechanism is on the same order of magnitude as that of the interaction-induced term originally included in the DID mechanism. The signs and the magnitudes of the intensity changes induced by the newly added term are discussed. (C) 2002 Elsevier Science B.V. All rights reserved.