A density functional theory study of CF3CH2I adsorption and reaction on Ag(111)

The adsorption and reaction behaviors of CF3CH2I on Ag(111) were systematically studied by density functional theory (DFT) calculations. Physical adsorption of CF3CH2I on Ag(111) occurs due to the weak interactions between surface Ag atoms and iodine atom of CF3CH2I; while strong chemisorption occurs for CF3CH2 fragment on Ag(111). Electronic analysis indicates that the singly occupied molecular orbital (SOMO) of CF3CH2 strongly interacts with the surface Ag atoms. It is very interesting to find that the most stable structures of CF3CH2 on Ag(111) locate at the top site, instead of the hollow sites. This might be attributed to the facts that CF3CH2 adsorbed at the top site will maximize the sp3-type hybridization, and the possible weak interaction between the fluorine lone pair electrons of p orbitals for CF3CH2 and surface Ag(111) occurs, which is supported by the charge density difference (CDD) analysis with a low isosurface value. We propose that the charge density difference (CDD) analysis with a high or low isosurface value can be widely applied to analyze the strong or weak electronic interactions upon adsorption. Transition state calculations suggested that the energy barrier of CF bond rupture for CF3CH2I on Ag(111) (1.44 eV) is much higher than that of CI bond breakage for CF3CH2I (0.43 eV); and the activation energy of the CF bond dissociation for CF3CH2(a) is 0.67 eV.