ULTRAFAST TIME-RESOLVED INFRARED PROBING OF ENERGY-TRANSFER AT SURFACES

Picosecond and femtosecond infrared techniques are used to characterize vibrational energy transfer rates and provide novel insights into the relaxation of non-equilibrium energy distributions. For adsorbates on metal surfaces, it is essential to determine the absolute coupling strengths between different degrees of freedom, i.e., vibrational modes and low-lying electronic states. In the present work, the spectral shift of the CO stretch has been used to follow the temporal evolution of the adlayer response as a consequence of ultrashort infrared, visible, and ultraviolet excitation of the underlying metal. Results from CO/Pt(111) and CO/Cu(100) will be presented, their differences will be discussed, and comparison will be made to current theoretical models of the damping rates.