Theoretical Calculations of Dissociative Adsorption ofCH4on an Ir(111) Surface

The activation energy for chemisorption of ${\mathrm{CH}}_4$ at an Ir(111) surface is determined using density functional theory combined with an estimate of the long range dispersion interaction. The results are found to be in good agreement with published results of bulb and beam experiments analyzed with a precursor model. A surprisingly large surface relaxation is found where an Ir surface atom is displaced outwards by as much as 0.6 Å. A strongly bound molecular state at kinks and adatoms involving ${\eta }^2-\mathrm{H},\mathrm{H}$ bonding was also found.