The Influence of a Changing Local Environment during Photoinduced CO 2 Dissociation

Though largely influencing the efficiency of a reaction, the molecular‐scale details of the local environment of the reactants are experimentally inaccessible hindering an in‐depth understanding of a catalyst's reactivity, a prerequisite to maximizing its efficiency. We introduce a method to follow individual molecules and their largely changing environment during a photochemical reaction. The method is illustrated for a rate‐limiting step in a photolytic reaction, the dissociation of CO 2 on two catalytically relevant surfaces, Ag(100) and Cu(111). We reveal with a single‐molecule resolution how the reactant's surroundings evolve with progressing laser illumination and with it their propensity for dissociation. Counteracting processes lead to a volcano‐like reactivity. Our unprecedented local view during a photoinduced reaction opens the avenue for understanding the influence of the products on reaction yields on the nanoscale.