Electronic structure of 1,3,5-triaminobenzene trication and related triradicals: Doublet versus quartet ground state J. Chem. Phys. 122, 154308 (2005); 10.1063/1.1855882 Time evolution of the lowest singlet states of Z-1,3,5-hexatriene and 1,3-cyclohexadiene studied by femtosecond photoionization AIP Conf.The electronic structures of non-Kekule-type isoelectronic molecules 1,3,5-trimethylenebenzene (TMB) and 1,3,5-triaminobenzene trication (TAB3+) having a threefold axis are discussed with the ab initio molecular orbital (MO) method. The quartet state with a D3h geometry is predicted to be the ground state of TMB and T AB3+. According to the Jahn-Teller theorem, the doublet 2 E" states of TMB and T AB3+ are subject to the first order distortions which remove the degeneracy. The quartet-doublet energy splittings are calculated for these non-Kekule-type molecules at the second order M011er-Plesset (MP2) perturbation level of theory. In TMB the 4A~ state with a planar D3h geometry is predicted to lie well below the 2 A2 state with a planar C 2v geometry in which one of the methylene groups has a longer C-C bridge-bond connecting with the benzene ring. Moreover, in TAB3+ the 4A; state with a planar D3h geometry also lies well below the 2A2 state. The 2A2_2 B1 energy splittings on the 0 pseuclorotationpotential surface overestimated at the unrestricted Hartree-Fock (UHF) level are_corrected with the MP2 method.
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