Abstract: Adsorption of oxygen on Rh(111)

The adsorption of oxygen on Rh(111) at approximately 100 K has been studied by thermal desorption mass spectrometry (TDS), Auger electron spectroscopy (AES), and low energy electron diffraction (LEED). Oxygen adsorbs in a disordered state at 100 K and orders irreversibly into an apparent (2 x 2) surface structure upon heating to T ≥ 150 K. The kinetics of this ordering process have been measured by monitoring the intensity of the oxygen (1,1/2bar) LEED beam as a function of time with a Faraday cup collector. The kinetic data fit a model in which the rate of ordering of oxygen atoms is proportional to the square of the concentration of disordered species due to the nature of adparticle interactions in building up an island structure. The kinetic data are shown in Fig 1 for five temperatures at which the ordering was measured, where f(N0) is the integrated form of the kinetic rate law. On the basis of these data, the activation energy for ordering is 13.5±0.5 kcal/mol. This is consistent with values reported for oxygen ordering on Ir(111), 16-19 kcal/mol [1], and for oxygen migration on Ru, 14 kcal/mol [2]