title: Gas phase UV spectrum of a Cu(II)-bis(benzene) sandwich complex: experiment and theory.
abstract: Photofragmentation with tunable UV radiation has been used to generate a spectrum for the copper-bis(benzene) complex, [Cu(C6H6)2](2+), in the gas phase. The ions were held in an ion trap where their temperature was reduced to ∼150 K, whereby the spectrum revealed two broad features at ∼38,200 and ∼45,700 cm(-1). Detailed calculations using density functional theory (DFT) show the complex can occupy three minimum energy structures with C2v and C2 (staggered and eclipsed) symmetries. Adiabatic time-dependent DFT (TDDFT) has been used to identify electronic transitions in [Cu(benzene)2](2+), and the calculations show these to fall into two groups that are in excellent agreement with the experimental data. However, the open-shell electronic configuration of Cu(2+) (d(9)) may give rise to excited states with double-excitation character, and the single-excitation adiabatic TDDFT treatment leads to extensive spin contamination. By quantifying the extent of spin contamination and allowing for the inclusion of a small percentage (∼10%), the theory can provide quantitative agreement with the experimental data.
authors.affiliation: Department of Physical and Theoretical Chemistry, School of Chemistry, University of Nottingham , University Park, Nottingham NG7 2RD, United Kingdom.
authors.forename: Lifu
authors.initials: L
authors.lastname: Ma
authors.forename: Joseph
authors.initials: J
authors.lastname: Koka
authors.forename: Anthony J
authors.initials: AJ
authors.lastname: Stace
authors.forename: Hazel
authors.initials: H
authors.lastname: Cox
mesh_terms: D001554:Benzene / Q000737:chemistry*; D003300:Copper / Q000737:chemistry*; D005740:Gases / Q000737:chemistry*; D008956:Models, Chemical; D055668:Photochemical Processes; D013057:Spectrum Analysis; D014466:Ultraviolet Rays
chemical_list: D005740:Gases; D003300:Copper; D001554:Benzene