The electronic spectra of aryl olefins: A theoretical study of phenylacetylene

The electronic absorption and emission spectra of phenylacetylene have been studied by means of a multiconfigurational second-order perturbation method and its multistate extension. The low-lying valence singlet and triplet π→π* excited states together with 3s3p3d members of the two lowest Rydberg series have been computed in the vertical spectrum. By optimization of the geometries of the ground and low-lying excited states and the calculation of transition energies and properties, the obtained results lead to a detailed analysis and assignment of the available experimental absorption spectrum and to the description of the basic features of the emission processes in phenylacetylene. Vibrational frequencies for the two lowest singlet and triplet excited states have also been computed. The spectroscopy of phenylacetylene is finally related to that of other aryl olefins such as styrene and benzaldehyde. Differences and similarities of their excited state structures are discussed.