Photoemission into water adsorbed on metals: Probing dissociative electron transfer using theory

The photoinduced dissociation of water adsorbed on a silver nanoparticle is explored using theory to probe reaction pathways that produce hydrogen. Ab initio configuration theory is used to describe the systems. A formulation that allows excited electronic states embedded in a near continuum of lower energy states to be calculated accurately is described. Electron attachment of a photoemitted electron to adsorbed water can lead to the formation of H 2 at a very low energy barrier with oxygen remaining on the Ag surface. A large energy barrier to form H 2 plus adsorbed O is found for the ground state. The excited state has a much smaller barrier to OH stretch; however, to dissociate, the system must cross over from the excited state to the ground state potential energy surface. The cross over point is near the transition state for a ground state process. A characteristic feature of the excited state potential curve is an increase in energy in the early stages of OH stretch as the charge transfer state evolves from a state with considerable Rydberg character to one that has a typical OH antibonding molecular orbital. Another pathway releases a H atom leaving OH on the surface. Effects due to doping of a Ag nanoparticle with a K electron donor atom are compared with those caused by a Fermi level shift due to an applied potential. Results are also reported for electron transfer to a solvated lithium ion, Li(H 2 O)   6 + , near the surface of a silver particle. A steering mechanism is found that involves the interaction of a hydridic hydrogen formed after electron transfer with an acidic hydrogen of a second solvated water molecule. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009