ИСТИНА

Electronic states of different multiplicity of (VBz)+ complexes (Bz = benzene) were investigated using high-level ab initio methods. Gaussian basis sets 6-31G(d) and 6-311++G(d,p) were used for H and C atoms, while Stuttgardt RSC 1997 ECP from EMSL Basis Set Library and all electron QZVPP basis set of Ahlrichs were used for V atom. Geometry optimization was carried out at CASSCF level. An active space consisting of two (π and π*) pairs of benzene orbitals and 3d, 4s, and 4p orbitals of V (13 orbitals in total with eight active electrons). It was shown that the (3d, 4s, 4p) model space as well as the multiconfigurational quasidegenerate perturbation theory (MCQDPT) level accounting for the dynamic electron correlation provide excitation energies of V+ close to the experiment. The quintet state was found to be the ground electronic state with a slightly distorted equilibrium configuration of C6v symmetry. Singlet and triplet (VBz)+ complexes are distorted significantly, forming a C2v structures with two para-carbon atoms to be closer to V that the others. These distortions are caused by the Jahn-Teller effect of the first order, since the ground state of the C6v singlet and triplet complexes are degenerate. (VBz)+ complexes of the other distortion type, namely, when two para-carbons are farther from vanadium than others, are transition states at the all multiplicity states. Dissociation energies (EV-Bz) of all (VBz)+ multiplicity states with respect to the (V+ + C6H6) dissociation limit were evaluated at MCQDPT level for the CASSCF optimized geometries. Also EV-Bz values were obtained for the partially relaxed structures. It was shown that EV-Bz estimates for the quintet state with and without ZPE correction are close to the experimental ones. In contrast to the EV-Bz value for the quintet state, EV-Bz for both singlet and triplet states are higher by 25-30 kcal/mol. An electronic structure of the (VBz)+ complexes of different multiplicity and its effect on the binding energy was also analyzed.