Symmetry adapted cluster‐configuration interaction study on the excited and ionized states of TiBr₄ and TiI₄

The symmetry adapted cluster‐configuration interaction (SAC‐CI) method is briefly reviewed and applied to the excitation and ionization spectra of TiX₄ (X=Br, I). The valence excited states of these molecules are investigated systematically and compared with the previous study on TiCl₄. The experimental spectra are well reproduced and assigned by the SAC‐CI calculation including spin–orbit interaction of the ligand p atomic orbital (AO) and Ti d AO. Nine A₁, ten A₂, 20 E, and 30 T₁ and T₂ states are calculated for the excited states, and the oscillator strengths are distributed among the transitions to 30 T₂ states, which cause the excitation spectra to be very complicated, especially for the TiI₄ molecule. The ordering of the ionized states in the outer valence region is (1t₁)⁻¹<(3t₂)⁻¹<(1e)⁻¹<(2t₂)⁻¹< (2a₁)⁻¹, which is the same as that of TiCl₄. The spin–orbit splittings in the ²T₂ states of TiBr₄ and TiI₄ are estimated to be smaller than those of the previous studies, and we propose a new assignment for the experimental photoelectron (PE) spectra.