title: Ab initio molecular orbital study of ground and low-lying electronic states of CoCN.
abstract: The ground and low-lying excited states of CoCN have been studied by ab initio multireference single and double excitation configuration interaction (MR-SDCI) calculations with Davidson's correction Q and Cowan-Griffin's relativistic corrections. The electronic ground state of CoCN is (3)Phi(i) and the equilibrium geometry is linear with bond lengths of r(e)(Co-C)=1.8540 A and r(e)(C-N)=1.1677 A, substantially different from the experimentally derived values of r(0)(Co-C)=1.8827(7) A and r(0)(C-N)=1.1313(10) A. The first excited state is (3)Delta(i), separated from the ground state by 727 cm(-1). Larger dynamical electron correlation energy for the low-spin (3)Phi state than for the high-spin (5)Phi state makes the (3)Phi state to be the ground state, which is discussed in terms of the differences in natural orbitals. A new spin-orbit interaction scheme between the X (3)Phi(i) and 1 (3)Delta(i) states is proposed.
authors.affiliation: Department of Chemistry, Faculty of Science, Ochanomizu University, 2-1-1 Otsuka, Bunkyo-ku, Tokyo 112-8610, Japan. hirano@nccsk.com
authors.forename: Tsuneo
authors.initials: T
authors.lastname: Hirano
authors.forename: Rei
authors.initials: R
authors.lastname: Okuda
authors.forename: Umpei
authors.initials: U
authors.lastname: Nagashima
authors.forename: Per
authors.initials: P
authors.lastname: Jensen