The tip of a scanning tunnelling microscope (STM) can be viewed as a highly localized electron beam, whose energy can be tuned by the applied voltage. The inelastic part of this electron beam might excite vibrations of surfaces or of adsorbed molecules. By this, it is possible to measure vibrations and to induce chemical reactions. Implementation of this method demands imaging at low temperature (5K) with submolecular resolution, in order to identify molecular side groups and position the tip exactly above a specific part of the molecule. In this talk, I will present vibrational spectra of individual water molecules adsorbed on Au(111) and the pure Au(111) surface. The reaction is exemplified on the rearrangement of hydrogen bonds within ice clusters and on the isomerisation of substituted benzene molecules. The energy dependence of the induced reactions allows determination of the excitation mechanism. Femtosecond laser pulses are a second means to produce high energetic electrons close to adsorbed molecules. The combination of a femtosecond laser with a STM allows investigating reactions locally. This will be demonstrated for CO/Cu(111).