Quantum size effect on the dissociation of O2 molecules on ultrathin Pb(111) films
Abstract
Using first-principles calculations, we systematically study the dissociation of O2 molecules on different ultrathin Pb(111) films. Based on our previous work revealing the molecular adsorption precursor states for O2, we further explore that why there are two nearly degenerate adsorption states on Pb(111) ultrathin films, but no precursor adsorption states exist at all on the Mg(0001) and Al(111) surfaces. And the reason is concluded to be the different surface electronic structures. For the O2 dissociation, we consider both the reaction channels from gas-like and molecularly adsorbed O2 molecules. We find that the energy barrier for O2 dissociation from the molecular adsorption precursor states is always smaller than from O2 gases. The most energetically favorable dissociation process is found to be the same on different Pb(111) films, and the energy barriers are found to be modulated by the quantum size effects of Pb(111) films.