Often essential ingredients is to probe transient intermediates and molecular states close to the transition state where lifetimes are extremely short. It is therefore necessary to perform experiments using ultrafast techniques. To perform our experiments we use a laser “pump” pulse to provide energy to the system in a controlled manner with well-defined temporal characteristics. The energy from the laser pulse creates energetic electrons and phonons in the surface of the catalyst. Energy transfer to the adsorbed reactants can place the reactants into transiently excited states which could allow a reaction or transition to occur. X-ray “probe” pulses from an x-ray free electron laser with a controlled delay from the initial laser pulse can then be used to produce detectable photons or electrons from the system. The energy distribution of the particles produced will be a function of the initial and final electronic states of the reactants. By analysing the energy distribution of the emitted particles as a function of the pump-probe delay time we can measure changes in the electronic states of the reactants on ultrashort timescales. This can help to reveal short-lived intermediate states that may be necessary for a reaction to proceed, this information could be used to uncover the mechanisms behind certain reactions and to potentially design more efficient catalysts.