The electronic states of the azines. V. Pyridazine, studied by VUV absorption, near threshold electron energy-loss spectroscopy and ab initio multi-reference configuration interaction calculations

A comparison of VUV absorption with near-threshold electron energy-loss spectra, has led to the identification of several new low-lying electronic states of pyridazine. The assignment of these and previously known singlet states is discussed in the light of large-scale all-valence electron CI calculations using a multi-reference, multi-root CI (MRDCI) study, which includes Rydberg orbitals in the basis set. The UV-photoelectron spectrum is reconsidered in the light of these calculations and it is concluded that IP₂ is of ²B₁ rather than ²A₂ symmetry. The ground state molecular electronic properties are evaluated with a large SCF/CI basis, and compared with available experimental data. © 1991.