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 tem perature. The initial sticking probability can be increased by an orde r 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 observe d for all surface temperatures from 300 to 600 K-, a sharp enhancement of the sticking probability is seen at around 550 K for energies abov e 0.6 eV. A direct (rather than precursor-mediated) activated adsorpti on 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.