The microscopic diffusion processes of NO molecules on Pt(997) at low coverage were investigated using time-resolved infra-red reflection absorption spectroscopy. When NO molecules adsorbed on Pt(997) at low temperature, each molecule transiently migrated on the surface from the first impact point to a possible adsorption site. At 11K, the molecules were trapped at 4 adsorption sites on Pt(997): the on-top sites on the (111) terrace, the hollow sites on the (111) terrace, the bridge sites at the step and the hollow sites at the step downstream. Based upon the initial population ratio for these sites, the mean lateral displacement by transient migration was estimated to be 4.1Å. By heating the surface to 45K, the hollow site species migrate up to the bridge sites; the migration barrier was roughly estimated to be 120meV. At 70 to 77K, time-resolved infra-red reflection absorption spectroscopic measurements were carried out to observe the site change of (111) terrace species to the adjacent (111) terrace sites at isothermal conditions; the activation barrier and the pre-exponential factor were estimated to be 200meV and 2.0 x 1011/s, respectively. At 100 to 110K, the (111) terrace species migrated across the terrace and finally reached the bridge sites. The activation barrier between the (111) terrace sites and the pre-exponential factor were estimated to be 290meV and 6.5 x 1011/s, respectively, from the time-resolved infra-red reflection absorption spectroscopy data together with kinetic Monte Carlo simulations. On the whole, the quantitative microscopic picture of NO migration on Pt(997) was established.

Microscopic Diffusion Processes of NO on the Pt(997) Surface. N.Tsukahara, K.Mukai, Y.Yamashita, J.Yoshinobu: Journal of Chemical Physics, 2008, 128[5], 054701