Adsorption of C2H radical on cobalt clusters: anion photoelectron spectroscopy and density functional calculations

A theoretical study of the oxidation of benzene by manganese oxide clusters: formation of quinone intermediates

Manganese oxides (MnxOy) have been widely applied in various chemical industrial processes owing to their long lifetime, low cost and high abundance. They have been used as co-reactants for the elimination of volatile organic compounds (VOCs); however, their oxidation mechanism is not clearly established. In this theoretical study, interaction capacities between benzene (C6H6) and MnxOy clusters, which were modeled with MnO2 and Mn2O3 molecules, were investigated by quantum chemical computations using density functional theory (DFT) with the PBE-D3 functional. The interaction capacity between C6H6 and MnxOy was evaluated, and the probing of the initial stage of the C6H6 oxidation at a molecular level offers an in-depth oxidation reaction path. Interaction energies computed in several spin states, along with the analysis of the electron distribution using the quantum theory of atoms in molecules, natural bond orbital and Wiberg bond index techniques as well as local softness values and MO energies of fragments, point out that the interaction between C6H6 and Mn2O3 is stronger than that with MnO2, amounting to -43 and -35 kcal mol-1, respectively, and the metal atom is identified as the primary active site. During the oxide cluster-assisted oxidation, benzene firstly undergoes an oxidation reaction by active oxygen to generate intermediates such as hydroquinone and benzoquinone. The pathway involving p-benzoquinone as the product (noted as PR1) is the most energetically favored one through a transition structure lying at 19 kcal mol-1, below the energy reference of the reactants, leading to an energy barrier significantly lower than that of 36 kcal mol-1 found for the gas phase oxidation reaction with molecular oxygen without the assistance of the oxide clusters. Potential energy profiles illustrating the reaction paths and molecular mechanisms were described in detail.

Gas phase anion photoelectron spectroscopy and theoretical investigation of gold acetylide species

We conducted gas phase anion photoelectron spectroscopy and density functional theory studies on a number of gold acetylide species, such as AuC₂H, AuC₂Au, and Au₂C₂H. Based on the photoelectron spectra, the electron affinities of AuC₂H, AuC₂Au, and Au₂C₂H are measured to be 1.54(±0.04), 1.60(±0.08), and 4.23(±0.08) eV, respectively. The highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of AuC₂H and AuC₂Au are measured to be about 2.62 and 2.48 eV, respectively. It is interesting that photoelectron spectra of AuC₂H^- and AuC₂Au^- display similar spectral features. The comparison of experimental and theoretical results confirms that the ground-state structures of AuC₂H^-, AuC₂Au^-, and their neutrals are all linear with Au-C≡C-H and Au-C≡C-Au configurations. The similar geometric structures, spectral features, HOMO-LUMO gaps, and chemical bonding between AuC₂H^-/0 and AuC₂Au^-/0 demonstrate that Au atom behaves like H atom in these species. The photoelectron spectrum of Au₂C₂H^- shows that Au₂C₂H has a high electron affinity of 4.23(±0.08) eV, indicating Au₂C₂H is a superhalogen. Further, we found an unusual similarity between the terminal Au atom of Au₂C₂H^- and the iodine atom of IAuC₂H^-.

Photoelectron spectroscopy of CoC2H2(-) and density functional study of Co(n)C2H2 (n = 1-3) anion and neutral clusters

The anionic and neutral ConC2H2 (n = 1-3) clusters were investigated using anion photoelectron spectroscopy and density functional calculations. The adiabatic detachment energies and vertical detachment energies of ConC2H2(-) (n = 1-3) were determined. Our results show that the most stable geometries of anionic ConC2H2(-) (n = 1-2) and neutral ConC2H2 (n = 1-3) are composed of ConC2H clusters adsorbing a hydrogen atom on the top or bridge sites of Con, whereas Co3C2H2(-) consists of a five-member ring of Co3C2 carbide adsorbing two hydrogen atoms on two bridge sites of Co3. The reaction mechanisms show that the inserted isomer HCoC2H can convert into the vinylidene complex Co═C═CH2 via a side-on isomer M-η(2)-(C2H2).