The coadsorption of hydrogen and potassium on Ir(111)

The adsorption of gas-phase atomic hydrogen on potassium-precovered Ir(111) surfaces was investigated. Even very low coverages of potassium adatoms strongly inhibit the dissociative adsorption of molecular hydrogen. However, using gas-phase atomic hydrogen allows us to overcome the activation barrier for dissociative hydrogen adsorption. In addition, abstraction of hydrogen adatoms by impinging atomic hydrogen occurs. The probabilities and cross-sections for both reactions and the maximum number of hydrogen adsorption sites are derived and compared to data obtained on other surfaces. Furthermore, a kinetic isotope effect in the desorption of hydrogen and deuterium was observed. Implications of these results with respect to the potassium-hydrogen interaction are discussed.