Simulation of oxygen desorption from Pt(111)

Using the Monte Carlo technique, we simulate the kinetics of temperature-progammed associative desorption (TPD) of oxygen atoms from Pt(lll) at coverages below a quarter of the monolayer. Oxygen atoms are assumed to be adsorbed on a triangular lattice of fee sites. Nearest-neighbour (nn) O-O lateral interactions, epsilon(1), are considered to be strongly repulsive so that there are no occupied nn sites. The second- and third-nn interactions, epsilon(2)greater than or equal to 0 and epsilon(3)less than or equal to 0 (positive values correspond to repulsion), are chosen to reproduce the p(2x2) ordering of oxygen atoms. Comparison between the simulations and experimental TPD spectra for the O/Pt(lll) system is supporting repulsive O-O interactions. More specifically, the TPD spectra are hard to reconcile with the assumption that the O-O lateral interactions are partly attractive and that this attraction is sufficiently strong to stabilize the p(2 x 2) islands at low coverages and relatively high temperatures (similar to 400 K). The consequence of this finding for interpretation of available experimental data on oxygen diffusion on Pt(lll) is discussed in detail. (C) 1998 Elsevier Science B.V. All rights reserved.