Effect of oxygen impurities on a caesium-covered Mo(001) surface

The interaction dynamics of atomic and molecular oxygen with a caesium-covered molybdenum surface is studied within a semiclassical collision method in conjunction with a Potential Energy Surface derived by DFT-D calculations. The surface exposed to a flux of oxygen atoms is immediately covered, as the only occurring process is the adsorption one, independently of impinging energy value. On the other hand, the incidence of molecules gives rise to three different competitive surface processes according to the molecule’s collisional energy: molecular adsorption, inelastic molecular scattering, inelastic atomic scattering. The interaction mechanism is highlighted and related to potential anisotropy. O2 molecules, initially in the ground roto-vibrational state, are mostly inelastically scattered in the same vibrational level, while the final rotational distributions extend to the complete rotational ladder. Vibrationally excited molecules can attenuate the oxygen adsorption detrimental effect because they trigger energy exchanges that favour molecular scattering.