Diffusion of oxygen on the Re(20(2)over-bar1) plane

The diffusion of oxygen on the Re(20 (2) over bar 1) plane was studied by the held emission fluctuation method. At low coverages E = 22 kcal/mol, decreases to 16 kcal/mol at theta = 0.3, and increases to 25 kcal/mol at theta greater than or equal to 0.6. Mean square fluctuations are nearly temperature independent. It is argued that this behavior implies stronger effects of neighboring O atoms on diffusion saddlepoints than on occupied binding sites, and can be explained qualitatively by assuming that a single neighbor to a saddlepoint lowers E. while two neighbors on opposite sides raise it.