Experiments were performed with an Omicron STM1 microscope operating at room temperature and a base pressure of approximately 1×10⁻¹⁰ mbar. Si(111)-7×7 samples, tungsten tips and toluene molecules were prepared following the procedures outlined in reference 16 of the associated paper. The Si(111)-7×7 surface reconstruction was obtained from pre-cut Si(111) samples (n-type, phosphorus doped, 0.001–0.002 Ω cm) by repeated resistive heating to 1250°C. Tungsten tips were etched in a 2 M NaOH solution and out-gassed in vacuum to remove any tungsten-oxide. Toluene was purified by the freeze-pump-thaw technique with liquid nitrogen and checked for purity with a quadrupole mass spectrometer. We chose toluene for this study because of its thermal stability at room temperature, its ease of STM-induced molecular desorption, and its lack of STM current induced intramolecular bond breaking. To prepare a partially toluene covered surface (approximately 3 molecules per unit cell) the Si(111)−7×7 surface was dosed through a computer-controlled leak valve. Stability during the injection was ensured by a drift-compensation software which limited sample drift to between 100 fm/s and 10 pm/s in each of the x, y and z directions. All voltages are applied to the sample with the tip grounded through a Femto pre-amplifier.