Structure of the excited biacetyl molecule and analysis of its absorption and fluorescence spectra

A structural-dynamical model of biacetyl and biacetyl-d ₆ molecules in the excited electronic state is derived on the basis of semiempirical correlations and the method of hybrid atomic orbitals. The vibrational structure of absorption and fluorescence spectra is calculated in satisfactory agreement with experimental data. Interpretation of the lines is corrected. The effect of variations in the molecule valence angles, caused by electronic excitation, on the intensity of vibrational components is ascertained. A possibility of calculating relatively small structural and spectral variations resulting from methyl substitution in the sequence of glyoxal, methylglyoxal, and biacetyl molecules is demonstrated.