Abstract

The dynamics of the energy transfer processes at surfaces is of fundamental importance for a microscopic understanding of chemical reaction at solid surfaces, e.g. in heterogeneous catalysis. In conventional chemistry where phonons and electrons are always in thermal equilibrium, no detailed information can be obtained on the pathway of the energy flow between the substrate and the adsorbate. However, when a metal substrate is excited by an intense femtosecond laser pulse, a transient non-equilibrium of the electronic and phononic temperatures is created, which lasts on the order of the electron-phonon coupling time (for ruthenium ~1 ps) and allows to distinguish electron-mediated from phonon-mediated reactions [1]. The appropriate experimental approach is to measure the two-pulse correlation (2PC) of the respective reaction yield. To this end, the fundamental output of an amplified Ti:sapphire femtosecond laser system is split in two equally intense portions and then both beams are sent time-delayed onto the sample mounted in ultrahigh vacuum chamber. The yield of the desorbed product species is detected with a quadrupole mass spectrometer as a function of the pulse-pulse delay.

© 2002 Optical Society of America