The electronic states and molecular properties of 1,2,3-triazine studied by VUV absorption, near-threshold electron energy-loss spectroscopy and ab initio multi-reference configuration interaction studies

Optical electronic absorption spectra, and electron energy-loss spectra have been obtained for 1,2,3-triazine. The valence and Rydberg excited states have been studied by multi-reference multi-root configuration interaction studies using MRD-CI techniques, and the results related to the experimental spectra. A number of Rydberg states, associated with five ionisation limits, have been identified along with valence states of types ^{1, 3}np* and ^{1, 3}pp*. The UV-photoelectron spectrum has been reconsidered by means of MRD-CI, Green's function and the non-diagonal TDA method; the first five IPs are as previously determined. This leads to the ionisation order:²A₁(11a^-1₁)< ²B₂(7b^-1₂)<²B ₁(2b^-1₁)<²A₂(1a ^-1₂)<²A₁(10a^-1₁) .The electronic properties of the molecule have been determined at the equilibrium geometry for a large basis set at both the SCF and MP2 levels.