PPP and CNDO calculations for protonated molecules

CNDO calculations have been used to obtain the one-centre core integrals for protonated azines required in calculating the π→π* absorption spectra of such molecules using the PPP method. Calculated spectra for both the parent and the protonated molecules are obtained in satisfactory agreement with experiment. The changes in the σ-framework of the molecules on protonation are also discussed in terms of the CNDO results. © 1970 Springer-Verlag.