Vibrational response of surface adsorbates to femtosecond substrate heating

The transient response of the internal stretch vibration of CO molecularly adsorbed on Cu ( 111) has been measured following the impulsive (300 fs) excitation of electrons in the underlying metal substrate by a visible light pulse. It is proposed that the stretch vibration couples indirectly to substrate phonon and electron reservoirs via the frustrated translational surface mode. The couplings to the bulk electron reservoir with a rate yc = 167(24) GHz, and to the bulk phonon reservoir with a rate y,_ = 145 (56) GHz were measured. The experiments represent an important step towards surface control of specific states of molecular adsor-bates near their desorption threshold. 1