DOI: 10.15125/bath-01363
title: Dataset for "Measuring competing outcomes of a single-molecule reaction reveals classical Arrhenius chemical kinetics"

description: This dataset contains data supporting the results presented in the paper "Measuring competing outcomes of a single-molecule reaction reveals classical Arrhenius chemical kinetics". It contains the analysed data of single toluene molecule manipulation experiments carried out on the Si(111)-7x7 surface in Excel spreadsheet format. The experiments span the injection bias voltage range of +1.4 eV to +2.2 eV, the injection current range of 25 pA to 900 pA, and three separate injection locations: on top of an adatoms, a molecule, and a restaom. The dataset contains the extracted manipulation probabilities and branching ratios as well as spectroscopy data above faulted corner and toluene faulted middel sites.

The atomic resolution of scanning probe microscopy and its ability to excite a molecule locally can give control over the probability of inducing a single-outcome single-molecule reaction.  The paper shows our control over the branching ratio between a single-molecule reaction that exhibits two reaction outcomes. Toluene molecules chemisorbed on the Si(111)-7x7 surface at room temperature are induced to react, one at a time, by the tunnelling current of a scanning tunnelling microscope: the molecule either desorbs, or switches to an adjacent surface site. Above a voltage threshold set by the electronics structure of the molecule, we see that the branching ratio between these two outcomes is dependent on the excess energy the exciting electron carries. Using known values and ab inito DFT calculations support our findings, a simple Arrhenius model is developed to describe the intermediate physisorbed state that leads to either desorption or site-switching. We conclude that the excess energy of the exciting electron leads to a heating of the intermediate physisorbed state and hence, via their energy barrier and pre-factors, gives control over the two reaction outcomes.
description: 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.
description: Full details of how the data were processed may be found in the supplementary text of the paper.
description: The dataset is in Excel (Office Open XML) spreadsheet format.
description: The data used to plot each figure in the paper is provided on a separate sheet in the Excel workbook. The raw experimental data is also included on separate sheets.