Calculations on the orientation on the fragment in Co 3(CO) 9(μ 3-CH): Implications for metal surfaces

Abstract

Abstract A series of molecular orbital calculations using the Fenske-Hall method have been carried out on Co 3 (CO) 9 (μ 3 -CH), in which the orientation of the CH fragment is varied with respect to the triangular plane of the three Co atoms. The calculations show that the energy differences between the orbitals that are predominantly CH in character are affected very little by the orientation of the CH fragment. These calculated differences are Δ (2 σ −1 σ )≅7 eV and Δ (1 π −1 σ )≅ 10.5 eV. The calculated splitting of the degenerate 1π orbitals for geometries with tilted CH fragments never amounted to more than 0.46 eV. Mixing of CH orbitals into the predominantly Co 3d manifold was extensive in all of the calculations. These calculations provide no support for the interpretation of energy loss and photoemission electron spectroscopy experiments in terms of CH fragments that are tilted with respect to the metal surface, but such an interpretation cannot be eliminated due to the diffuse nature of the spectral bands in the photoemission experiments.