Desorption of CO from Ru(001) induced by near-infrared femtosecond laser pulses

Irradiation of a Ru(001) surface covered with CO using intense femtosecond laser pulses (800 nm, 130 fs) leads to desorption of CO with a nonlinear de pendence of the yield on the absorbed fluence (100-380 J/m(2)). Two-pulse c orrelation measurements reveal a response time of 20 ps (FWHM). The lack of an isotope effect together with the strong rise of the phonon temperature (2500 K) and the specific electronic structure of the adsorbate-substrate s ystem strongly indicate that coupling to phonons is dominant. The experimen tal findings can be well reproduced within a friction-coupled heat bath mod el. Yet, pronounced dynamical cooling in desorption, found in the fluence-d ependence of the translational energy, and in a non-Arrhenius behavior of t he desorption probability reflect pronounced deviations from thermal equili brium during desorption taking place on such a short time scale. (C) 2000 A merican Institute of Physics. [S0021-9606(00)70122-X].