A time-domain study was made of the diffusion of CO on a vicinal Pt(111) surface at low substrate temperature induced electronically via substrate electrons, which were optically excited by femtosecond-laser pulses. Hopping rates from step sites to terrace sites were determined using optical second-harmonic generation as a sensitive probe of the step coverage. The dynamics of the electronic energy transfer between the excited substrate electrons and the adsorbate degrees of freedom were investigated by the application of a two-pulse correlation scheme. A non-linear dependence of the hopping rate upon the laser fluence (∝F6) was observed in a fluence range of 1.9 to 4.3mJ/cm2, and a narrow two-pulse correlation with a width of below 0.5ps that increased with increasing laser fluence. It was shown that the broadening of the two-pulse correlation with laser fluence was a general phenomenon for substrate-mediated laser-induced surface reactions.

Time-Domain Investigation of Laser-Induced Diffusion of CO on a Vicinal Pt(111) Surface. M.Lawrenz, K.Stépán, J.Güdde, U.Höfer: Physical Review B, 2009, 80[7], 075429