The intensity ratio of corresponding symmetric and antisymmetric stretching modes

The intensity ratio of corresponding symmetric and antisymmetric stretching modes is derived for C_2v and C_3v molecules, using the zero-order approximation of bond moment theory. The validity of the final relations is discussed with respect to the assumptions made. The relations could be helpful in the estimation of individual intensities in cases in which the frequencies of corresponding symmetric and antisymmetric modes nearly coincide.