G-intensity sum rule applications: XY3 molecules

Using the pyramidal XY3 (X=N, P; Y=H, F) molecules as examples, the G-intensity sum rule of Crawford, expressed in terms of effective charges, is shown to be an effective test of the numerical results of vibrational analyses. Errors in previously reported effective charge values for NF3 and PF3 are corrected. Values for the as yet unreported polar tensors of these molecules are presented. Comparisons of these results with those previously reported for other molecules are made.