Abstract

Ultrafast laser heating pulses create unique environments for surface chemistry on metal surfaces. Recent femtosecond experiments have shown, for example, that nonequilibrium substrate conditions can play a central role in laser induced desorption[1]. In these experiments extremely high electronic temperatures (4000 °K) are produced which modify adsorbates in a manner which is impossible to achieve via a conventional thermal process. Here we report the results of probing the internal vibrations of CO adsorbate molecules as a function of time following the impulsive excitation of electrons in the underlying Cu(111) substrate by 300 fs visible light pulses[2]. We find that a low frequency CO mode couples to substrate electrons and phonons, and that the representative coupling rates can be separately determined[2,3]. Importantly, with increased excitation of the substrate, our measurements provide indication of stronger, temperature dependent couplings between the adsorbate vibrations and the substrate reservoirs[4].

© 1994 Optical Society of America