Considerably Increased Dynamics of CO-Water Complexes over CO and Water Alone

Solvents are increasingly known to influence chemicalreactivity.However, the microscopic origin of solvent effects is scarcely understood,particularly at the individual molecule level. To shed light on this,we explored a well-defined model system of water (D2O)and carbon monoxide on a single-crystal copper surface with time-lapsedlow-temperature scanning tunneling microscopy (STM) and ab initiocalculations. Through detailed measurements on a time scale of minutesto hours at the limit of single-molecule solvation, we find that atcryogenic temperatures CO-D2O complexes are moremobile than individual CO or water molecules. We also obtain detailedmechanistic insights into the motion of the complex. In diffusion-limitedsurface reactions, such a solvent-triggered increase in mobility wouldsubstantially increase the reaction yield.

Automated summary

Solvents have been found to affect chemical reactivity, but the underlying microscopic mechanism is not well understood. This study investigates a model system of water and carbon monoxide on a copper surface using scanning tunneling microscopy and ab initio calculations. The results show that at low temperatures, CO-D2O complexes are more mobile than individual CO or water molecules. The study also provides insights into the detailed mechanism of complex motion. This increase in mobility induced by the solvent could significantly enhance the reaction yield in diffusion-limited surface reactions.