A theoretical study of CHx chemisorption on the Ni(100) and Ni(111) surfaces

Cluster model calculations have been performed for CH_x, x = 0?3, chemisorbed on Ni(100) and Ni(111). The predicted chemisorption energies, at the present level of theory, based on bond-prepared clusters for Ni(100) are for carbon 150 kcal/mol, for CH 136 kcal/mol, for CH₂ 91 kcal/mol and for CH₃ 46 kcal/mol. The corresponding energies for Ni(111) are for CH 120 kcal/mol, for CH₂ 88 cal/mol and for CH₃ 49 kcal/mol. These chemisorption energies lead to similar stabilities for all CH_x fragments on both Ni(100) and Ni(111). Large basis sets and multi-reference correlation treatments are found to be very important in particular for the multiply bonded species. The vibrational C-H stretching frequencies predicted for CH_x on Ni(111) are for CH 3054 cm^?1 (2980 cm^?1), for CH₂ 3204 cm^?1 and for CH₃ 2709 cm^?1 (2680 cm^?1), where the available experimental values are given in parent The predicted ionization spectra of adsorbed CH_x are also in general agreement with experimental findings.