Insight Into Spin-Orbital Interaction Using Mcscf Method: A Special Analysis Of The (1)Sigma(+)(G) Electronic State In C-2 And The Linear Polyacetylenic C-4 And C-6

The symmetry-broken wave function can transform the (1)Sigma(+)(g) state of C-2 from the classic double bonding to the quadruple bonding, where the transformed wave functions of phi(L) and phi(R) are singly occupied by two opposite-spinning electrons. In this article, the effective bond order (EBO) contribution of the fourth bond in C-2 is assessed through the overlap integral between phi(L) and phi(R), namely the value (0.60) is the EBO contribution of the fourth bond in the transformed scheme. Hence, the new EBO is 3.36, which is more equitable than the original EBO (2.15) in the traditional scheme. In addition, the singlet diradical character of the linear polyacetylenic C-4 and C-6 in the (1)Sigma(+)(g) state is addressed for the first time. No spin-polarized bonding exists in other linear C-2n clusters, because the ionic interaction in the polyacetylenic (1)Sigma(+)(g) state of C-4 is negligible. Moreover, the coupling energy between alpha and beta single electrons in C-4 is only 4.0 kcal mol(-1) based on the electron spin-flip energy. (c) 2019 Wiley Periodicals, Inc.