title: Quantum chemical study of the electronic structure of NiCH2 + in its ground state and low-lying electronic excited states.
abstract: The electronic structure of NiCH(2) (+), representative of transition metal carbene ions, is investigated by means of several methods of quantum chemistry. The relative stabilities of the four low-lying doublet electronic states ((2)A(1), (2)A(2), (2)B(1), and (2)B(2)) are determined at the coupled cluster singles and doubles level (CCSD) and triples level [CCSD(T) and CCSDT-3] with both a Hartree-Fock and density functional theory (Kohn-Sham) reference. The equation-of-motion coupled cluster for treatment of excited states in singles and doubles approximation (EOM-CCSD) is used to characterize the transition energies from the (2)A(1) electronic ground state to the low-lying doublet excited states. The (2)A(2) and (2)B(1) states are nearly degenerate, found to be separated by 940 cm(-1) at the EOM-CCSD level, in agreement with the CASSCF energy ordering. The (2)B(2) state is calculated to be higher in energy by more than 1.0 eV. The spin purity of the low-lying doublet and quadruplet states described by CCSD calculations based on the unrestricted open-shell Hartree-Fock reference is discussed.
authors.affiliation: Laboratoire de Chimie Quantique UMR 7551 CNRS, Universite Louis Pasteur, 4 rue Blaise Pascal, 67000 Strasbourg, France.
authors.forename: Sébastien
authors.initials: S
authors.lastname: Villaume
authors.forename: Chantal
authors.initials: C
authors.lastname: Daniel
authors.forename: Alain
authors.initials: A
authors.lastname: Strich
authors.forename: S Ajith
authors.initials: SA
authors.lastname: Perera
authors.forename: Rodney J
authors.initials: RJ
authors.lastname: Bartlett