The electronic states of the azines. VII. 1,2,4-triazine, studied by photon absorption, near-threshold electron energy loss spectroscopy and ab initio multi-reference configuration interaction calculations Original Research Article

Ultraviolet photoelectron (UPS), ultraviolet (UV) and vacuum ultraviolet (VUV) absorption and electron energy loss (EEL) spectra are presented for 1,2,4-triazine in the gas phase and interpreted using the results of ab initio multi-reference configuration interaction calculations. The lowest optical band (1nπ∗, Emax≈3.1 eV) is highly structured. The corresponding triplet state is detected in EEL at 2.7 eV. Other valence states of type nπ∗ are assigned to EEL bands at 3.6 eV (1,3n π∗) and ≈6.0 eV(1nπ∗). The 1ππ∗ states are positioned about 5.0, 6.7, 7.8 and 7.9 eV, the last two relating to the benzene 1E1u state. Electron energy loss processes observed around 4.1 and 4.9 eV are attributed to excitation of 3ππ∗ states. Low-lying Rydberg states of type 1n3s and 1n3p have been assigned, but Rydberg series are not strong in the experimental spectra. The UPS has been interpreted by means of non-diagonal Greenʹs function and Tamm-Dancoff calculations.