title: Infrared spectra and quantum chemical calculations of the uranium carbide molecules UC and CUC with triple bonds.
abstract: Laser evaporation of carbon-rich uranium/carbon alloys followed by atom reactions in a solid argon matrix and trapping at 8 K gives weak infrared absorptions for CUO at 852 and 804 cm(-1). A new band at 827 cm(-1) becomes a doublet with mixed carbon 12 and 13 isotopes and exhibits the 1.0381 isotopic frequency ratio, which is appropriate for the UC diatomic molecule, and another new band at 891 cm(-1) gives a three-band mixed isotopic spectrum with the 1.0366 isotopic frequency ratio, which is characteristic of the linear CUC molecule. CASPT2 calculations with dynamical correlation find the C[triple bond]U[triple bond]C ground state as linear 3Sigma(u)+ with 1.840 A bond length and molecular orbital occupancies for an effective bond order of 2.83. Similar calculations with spin-orbit coupling show that the U[triple bond]C diatomic molecule has a quintet (Lambda = 5, Omega = 3) ground state, a similar 1.855 A bond length, and a fully developed triple bond of 2.82 effective bond order.
authors.affiliation: Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904-4319, USA.
authors.forename: Xuefeng
authors.initials: X
authors.lastname: Wang
authors.forename: Lester
authors.initials: L
authors.lastname: Andrews
authors.forename: Per-Ake
authors.initials: PA
authors.lastname: Malmqvist
authors.forename: Björn O
authors.initials: BO
authors.lastname: Roos
authors.forename: António P
authors.initials: AP
authors.lastname: Gonçalves
authors.forename: Cláudia C L
authors.initials: CC
authors.lastname: Pereira
authors.forename: Joaquim
authors.initials: J
authors.lastname: Marçalo
authors.forename: Claude
authors.initials: C
authors.lastname: Godart
authors.forename: Benjamin
authors.initials: B
authors.lastname: Villeroy