Direct observation of C2N2 uptake and dissociation on Pd(110) by fast high-resolution XPS

Abstract The full parameter space of C 2 N 2 adsorption and reaction on Pd(110) from 80 to 800 K has been mapped out by fast high-resolution XPS performed at the SuperESCA beamline of the ELETTRA synchrotron radiation facility in Trieste. Both C 1s and N 1s photoemissions have been followed continuously during exposure and on ramping the temperature, thus allowing direct observation of adsorption and of the dissociation of adsorbed species. The fraction of C 2 N 2 dissociated to CN increases from zero at 80 K to 100% at 220 K. Between these two extremes, dissociation is favoured at low coverages with the amount of coexisting intact C 2 N 2 species decreasing with temperature. The dissociation threshold is extrapolated to 90–100 K. Whereas only one surface configuration is detected for CN, two molecular C 2 N 2 monolayer species may be distinguished, which are distinct by way of their core level binding energies and associated with C 2 N 2 in symmetric (majority species) and less symmetric (minority species) adsorption geometries. The energetic parameters of the dissociation reaction have been estimated using the quantitative coverage information from temperature-programmed XPS and a simple model for the reaction kinetics.