Mode-softening of C-H stretch vibration in alkyl groups on Ag(1Â 1Â 1) and the fluorination effect

We demonstrate for the first time the fluorination effect on the C-H stretch mode-softening of alkyl groups on Ag(1 1 1), which provides the evidence that the partial charge-donation, instead of the formation of an agostic C-H ⋯ M bond, is responsible for the C-H stretch mode-softening of adsorbed hydrocarbons/alkyl fragments on transition metal surfaces.