Infrared Spectra and Quantum Chemical Calculations of the Uranium Carbide Molecules UC and CUC with Triple Bonds

摘要

Abstract: Laser evaporation of carbon-rich uranium/carbon alloys followed by atom reactions in a solidnargon matrix and trapping at 8 K gives weak infrared absorptions for CUO at 852 and 804 cm 1. A newnband at 827 cm 1 becomes a doublet with mixed carbon 12 and 13 isotopes and exhibits the 1.0381 isotopicnfrequency ratio, which is appropriate for the UC diatomic molecule, and another new band at 891 cm 1ngives a three-band mixed isotopic spectrum with the 1.0366 isotopic frequency ratio, which is characteristicnof the linear CUC molecule. CASPT2 calculations with dynamical correlation find the CtUtC ground statenas linearn3Σu with 1.840 Å bond length and molecular orbital occupancies for an effective bond order ofn2.83. Similar calculations with spin-orbit coupling show that the UtC diatomic molecule has a quintetn(Λ 5, Ω 3) ground state, a similar 1.855 Å bond length, and a fully developed triple bond of 2.82neffective bond order.