Electron energy-loss spectroscopy of excited states of the diazine molecules: Pyridazine

Excitation of the valence electronic states of the pyridazine molecules in the gas phase have been studied using the technique of electron energy-loss spectroscopy. Varying the electron scattering conditions, the residual electron energy and scattering angle, enabled the optically-allowed and-forbidden excitations to be differentiated. The measured energy-loss spectra enabled the vertical excitation energies of the observed states to be determined and tentative assignments for them to be obtained. Comparison of the available vertical excitation energies of the correlating triplet and singlet states of the diazine molecules, pyridazine, pyrimidine and pyrazine, allowed systematic trends in the energy shifts to be determined.