Tip-state control of rates and branching ratios in atomic manipulation.

We report the atomic manipulation properties of two distinct, stable, and reproducible states of a scanning tunneling microscope tip applied to chlorobenzene/Si(111)-(7x7). We show that the tip state influences the rates of (current-driven) molecular desorption and C-Cl dissociation as well as the branching ratio between these processes, but does not change the mediating electronic channel or the required number of electrons. These manipulation properties combined with the imaging properties of the two tip-states suggest the major difference between tip-states is their coupling efficiency to the pi-states of the chlorobenzene molecule.