Vibrational response of a chemisorbed molecule to femtosecond substrate heating

Subpicosecond laser heating pulses provide unique environments for surface chemistry on metal surfaces. This type of effect has been recently demonstrated in femtosecond desorption experiments.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. In this contribution, time resolved vibrational spectroscopy is used to monitor the response of molecularly adsorbed CO on Cu(111) following the excitation of the 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