Regensburg 2007 – scientific programme

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O: Fachverband Oberflächenphysik

O 57: Surface Chemical Reactions and Heterogeneous Catalysis II

O 57.6: Talk

Thursday, March 29, 2007, 17:00–17:15, H38

Ultrafast reaction dynamics of the associative desorption of C+O from Ru(001) — •Christian Frischkorn, Steffen Wagner, Henrik Öström, and Martin Wolf — Freie Universität Berlin, Fachbereich Physik, Arnimallee 14, 14195 Berlin

Femtosecond laser excitation of Ru(001) covered with atomic carbon and oxygen results in the recombinative desorption of CO molecules from the surface. A nonlinear fluence dependence of the reaction yield is found for excitation wavelengths of 400 and 800 nm. The higher reaction yield obtained for the 400-nm as compared to the 800-nm excitation can be attributed to the different optical penetration depths in Ru(001). As a consequence, higher surface temperatures rather than significant contributions of non-thermalized hot electrons cause the stronger laser-induced desorption with 400-nm pulses. Furthermore, the reaction mechanism of the CO recombination is investigated with two-pulse correlation measurements which exhibit a FWHM of ≈ 20 ps. However, despite this relatively wide two-pulse correlation (which usually is taken as an indication for a purely phonon-mediated energy flow), all experimental data are only consistently reproduced in the framework of frictional coupling between the substrate and the adsorbate, if both phonon and electronic contributions are included.