Adiabatic semi-empirical parametric method for computing electronic-vibrational spectra of complex molecules part 3. Azines

Abstract

Calculations of the excited state structure and absorption and emission spectra of azines (pyridine, pyrimidine, pyrazine and their deutero-substituted derivatives) were performed using the parametric method described previously. It is shown that the fragmentary approach for molecular model construction is suitable for heteroaromatic compounds with relatively small structural groups of the form H > C= and ▪ taken as primary fragments. Compared with H > C= the “first approximation model” of ▪ has an additional parameter of the σ-type that accounts for the peculiarities of the electronic density redistribution of n-π∗ transitions and affects primarily the changes in valence angles on excitation of the molecule. The major peculiarities of the vibrational structure of the experimental electronic spectra are well reproduced in the calculations and the parameters of the adiabatic molecular model obtained correlate well with the data estimated by other methods.