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

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