  We have investigated the quantum dynamics of O2 dissociative adsorption on a
Ag(111) surface. We performed the calculations with a Hamiltonian where the O2
translational motion is perpendicular to the surface and for O2 vibrational
energy. We found that dissociative adsorption occurs with an incident
translational energy below the expected activation barrier, while the
translational-energy dependence for adsorption probabilities is a smooth
sigmoid. Thus, there are non-negligible tunneling effects in the dissociative
adsorption that are affected by the activation barrier width. Moreover, the
incident translational energies at the inflection points of the adsorption
probabilities shift lower with increasing in vibrational quantum numbers of the
incident O2. Thus, there is significant energy transfer and coupling from
vibration to translational motion. The vibrational energy assists the O2
dissociative adsorption via a vibrationally assisted sticking effect.
