DYNAMICS OF O-2 ON PT(100)-HEX-R0.7-DEGREES - ACTIVATED ADSORPTION WITH A STRONG SURFACE-TEMPERATURE ENHANCEMENT

The dynamics of O2 dissociative adsorption on the reconstructed Pt(100)-hex-RO.7-degrees surface has been studied using supersonic molecular beams with variable gas translational energy and variable surface temperature. The initial sticking probability can be increased by an order of magnitude from 3 x 10(-4) at 0.07 eV and 300 K to 5 x 10(-3) at 0.9 eV and 600 K. A threshold energy of approximately 0.4 eV is observed for all surface temperatures from 300 to 600 K-, a sharp enhancement of the sticking probability is seen at around 550 K for energies above 0.6 eV. A direct (rather than precursor-mediated) activated adsorption mechanism is demonstrated and a dynamical (rather than stationary) PES model is used to account for some of the temperature enhancement. No measurable vibrational activation is observed, indicating that the barrier to dissociative adsorption is in the entrance channel.