Different processes are seen as relevant for the reaction rate enhancement of chemical reactions on optically excited metal nanoparticles. Recent studies suggest that all processes that follow a plasmon excitation, excited electrons, strong local fields and heat, can be of relevance for specific reactions. I will discuss a set of pump-probe experiments on gold nanoparticles in order to disentangle the processes. Calibrated optical transient absorption spectroscopy can constitute a thermometer for the electron gas and field sampling experiments address the coherent plasmon oscillation. Correlated with time-resolved reaction studies, this could provide a solid picture of plasmon-enhanced catalysis.