VIBRATIONAL RESPONSE OF SURFACE ADSORBATES TO FEMTOSECOND SUBSTRATE HEATING

The transient response of the internal stretch vibration of CO molecul arly adsorbed on Cu(111) has been measured following the impulsive (30 0 fs) excitation of electrons in the underlying metal substrate by a v isible light pulse. It is proposed that the stretch vibration couples indirectly to substrate phonon and electron reservoirs via the frustra ted translational surface mode. The couplings to the bulk electron res ervoir with a rate gamma(e) = 167 (24) GHz, and to the bulk phonon res ervoir with a rate gamma(L) = 145(56) GHz were measured. The experimen ts represent an important step towards surface control of specific sta tes of molecular adsorbates near their desorption threshold.