Figure 9: A schematic drawing for the estimation of transient diffusion length of NO on Pt(997). The shadowed regions and the other regions are regarded as the step region and the terrace region, respectively. and are an initial collision site and a final adsorption site, respectively. By considering the ratio of NO on the step to that on the terrace, the transient diffusion length can be estimated based on Buffon’s needle problem [2, 14].