The most common mechanism of catalytic surface chemistry is that of Langmuir and Hinshelwood (LH). In the LH mechanism, reactants adsorb, become thermalized with the surface, and subsequently react. The measured vibrational (relaxation) lifetimes of molecules adsorbed at metal surfaces are in the range of a few picoseconds. As a consequence, vibrational promotion of LH chemistry is rarely observed, with the exception of LH reactions occurring via a molecular physisorbed intermediate. Here, we directly detect adsorption and subsequent desorption of vibrationally excited CO molecules from a Au(111) surface. Our results show that CO (v = 1) survives on a Au(111) surface for ∼1 × 10-10 s. Such long vibrational lifetimes for adsorbates on metal surfaces are unexpected and pose an interesting challenge to the current understanding of vibrational energy dissipation on metal surfaces. They also suggest that vibrational promotion of surface chemistry might be more common than is generally believed.
Bibliographical noteFunding Information:
The authors thank A. Kandratsenka for discussions on CO vibrational lifetime estimation and T. Schäfer for his inputs regarding the CO/Au(111) TPD measurements. The authors acknowledge support from the Deutsche Forschungsgemeinschaft CRC1073 under project A04 and from the Ministerium für Wissenschaft und Kultur Niedersachsen and the Volkswagenstiftung under grant no. INST 186/901-1. A.M.W. and D.J.A. acknowledge support from the Alexander von Humboldt Foundation. D.J.A. acknowledges support from The International Center for Advanced Studies of Energy Conversion, Georg-August University of Göttingen. J.G. acknowledges support from the Max Planck – EPFL Center for Molecular Nanoscience and Technology. I.R. and A.M.W. acknowledge support from the Niedersächsisch-Israelische Gemeinschaftsvorhaben under project no. 574 7 022.