Executive Summary : | It is well understood that in precursor-mediated reactions on metal surfaces, where the reactants adsorb on the surface and subsequently undergo reaction, the adsorbates undergo rapid (few ps) thermalization and an equilibrium based description can be used to follow the progress of the reaction. However, in light of the recent discovery of unusually long lived vibrationally excited adsorbates, this viewpoint needs to be re-examined carefully. In the proposed work, using CO/Au(111) as a model system, we plan to measure the reaction probabilities of CO oxidation on O-covered Au(111) in a vibration state specific manner (v = 0, 1, 2), using molecular beam-surface scattering experiments. Vibrationally excited CO molecules produced using molecular beam and optical pumping methods will be used to prepare a well-defined, far from equilibrium population distribution and their reaction probabilities will be compared to ground state CO molecules. Vibrationally excited incident CO molecules will be prepared via infrared excitation using quantum cascade lasers (QCL) (v = 0 - 1) and home-built optical parametric oscillator/amplifier systems (OPO/A) (v = 0 - 2). Schemes for frequency stabilization of commercially available QCL and OPO/A systems meeting the stringent requirements of a molecular beam experiment (high intensity, narrow linewidth and high frequency stability) will be developed in the course of the proposed work. These measurements are expected to provide crucial insights into the reaction pathways of vibrationally excited adsorbates, an area which is largely unexplored, and at the same time put to test some of the foundational ideas of surface chemistry. In addition, the tools and methodology development proposed for vibration state specific preparation of incident molecules will provide a robust experimental platform for high resolution spectroscopy and quantum state selected scattering experiments in future. |