title: Infrared spectrum and bonding in uranium methylidene dihydride, CH2=UH2.
abstract: Uranium atoms activate methane upon ultraviolet excitation to form the methyl uranium hydride CH3-UH, which undergoes alpha-H transfer to produce uranium methylidene dihydride, CH2=UH2. This rearrangement most likely occurs on an excited-quintet potential-energy surface and is followed by relaxation in the argon matrix. These simple U+CH4 reaction products are identified through isotopic substitution (13CH4, CD4, CH2D2) and density functional theory frequency and structure calculations for the strong U-H stretching modes. Relativistic multiconfiguration (CASSCF/CASPT2) calculations substantiate the agostic distorted C1 ground-state structure for the triplet CH2=UH2 molecule. We find that uranium atoms are less reactive in methane activation than thorium atoms. Our calculations show that the CH2=UH2 complex is distorted more than CH2=ThH2. A favorable interaction between the low energy open-shell U(5f) sigma orbital and the agostic hydrogen contributes to the distortion in the uranium methylidene complexes.
authors.affiliation: Department of Chemistry, P.O. Box 400319, Charlottesville, Virginia 22904-4319, USA.
authors.forename: Jonathan T
authors.initials: JT
authors.lastname: Lyon
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: Tianxiao
authors.initials: T
authors.lastname: Yang
authors.forename: Bruce E
authors.initials: BE
authors.lastname: Bursten