THE ELECTRONIC STATES OF THE AZINES .7. 1,2,4-TRIAZINE, STUDIED BY PHOTON-ABSORPTION, NEAR-THRESHOLD ELECTRON-ENERGY-LOSS SPECTROSCOPY AND AB-INITIO MULTIREFERENCE CONFIGURATION-INTERACTION CALCULATIONS

Ultraviolet photoelectron (UPS), ultraviolet (UV) and vacuum ultraviol et (VU) absorption and electron energy loss (EEL) spectra are presente d for 1,2,4-triazine in the gas phase and interpreted using the result s of ab initio multi-reference configuration interaction calculations. The lowest optical band ((1)n pi, E(max) approximate to 3.1 eV) is h ighly structured. The corresponding triplet state is detected in EEL a t 2.7 eV. Other valence states of type n pi are assigned to EEL bands at 3.6 eV ((1,3)n pi) and similar to 6.0 eV ((1)n pi*). The (1) pi p i states are positioned about 5.0, 6.7, 7.8 and 7.9 eV, the last two relating to the benzene (1)E(lu) state. Electron energy loss processes observed around 4.1 and 4.9 eV are attributed to excitation of (3) pi pi states. Low-lying Rydberg states of type (1)n3s and (1)n3p have b een assigned, but Rydberg series are not strong in the experimental sp ectra. The UPS has been interpreted by means of non-diagonal Green's f unction and Tamm-Dancoff calculations.