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Shift and broadening of adsorbate vibrational modes
Affiliation:1. Anhui Laboratory of Molecule-Based Materials, Key Laboratory of Functional Molecular Solids, Ministry of Education, School of Chemistry and Materials Science, Anhui Normal University, Wuhu 241002, China;2. Institutes of Physical Science and Information Technology, Anhui University, Hefei, Anhui, 230601, China;1. Department of Chemistry, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran;2. Chemistry Department, Faculty of Sciences, Shahid Rajaee Teacher Training University, PO Box 16785 163 Tehran, Iran;3. Department of Forest Biomaterials, Organic Chemistry of Wood Components Laboratory, North Carolina State University, 2820 Faucette Drive, Raleigh, NC 27695-8005, United States;1. Department of Chemistry, Life Sciences and Environmental Sustainability and INSTM UdR Parma, University of Parma, Parco Area delle Scienze 17/A, 43124 Parma, Italy;2. SABIC Technology & Innovation, STC Geleen, Urmonderbaan 22, Geleen, the Netherlands;1. State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, PR China;2. College of Biological and Chemical Engineering, Guangxi University of Science and Technology, Liuzhou 545006, PR China;1. State Key Laboratory for Modification of Chemical Fibers and Polymer Materials, College of Materials Science and Engineering, Donghua University, Shanghai 201620, PR China;2. Key Laboratory of Synthetic Rubber, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, PR China
Abstract:The shift and broadening of the vibrational frequency of the adsorbate on a metal surface are calculated on the basis of two different models. The first model is an anharmonic one which includes multiphonon processes to all order in first-order perturbation theory. We show that anharmonic damping due to multiphonon processes is substantial for CO adsorbed on a Ni(100) surface and small for H adsorbed on a W(100) surface. At room temperature multiphonon processes with n > 2 are very important even in cases when the frequency of vibration of the adsorbate lies below twice the maximum phonon frequency of the substrate (n is the order of the process). For the CNi stretching mode of top-bonded CO on Ni(100) our results are in accord with the experimental data. The second model is an electronic one which includes the electron-hole pair loss mechanism. We show that the observed shift and broadening of the CO stretching vibration mode for a CO molecule adsorbed on Cu(100) and for a H atom adsorbed on a W(100) surface can be explained on the basis of this model. Variation of the shift and broadening of the CO stretching mode with the distance from a CO molecule to Ni(111) surface are calculated.
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