Communication: Fingerprints of reaction mechanisms in product distributions: Eley-Rideal-type reactions between D and CD3/Cu(111).

Through extensive direct dynamics studies of a prototypical Eley-Rideal type process, we demonstrate that fingerprints of microscopic reaction mechanisms can be identified in product distributions. Specifically, the umbrella vibration of CD4 formed by reacting gaseous D atoms with CD3 adsorbed on Cu(111) is highly excited if the reaction is initiated by a direct collision between the reactants due to the necessary inversion of the CD3 moiety. On the other hand, an indirect collision via a hot atom mechanism leads to much lower excitation in this product vibrational mode, and as such, an inversion is unnecessary. This fingerprint suggests an experimentally verifiable means to disentangle different mechanistic pathways.