Adsorbate Electronic Structure and Bonding on Metal Surfaces

Adsorbate Electronic Structure and Bonding on Metal Surfaces 

1 Stanford Synchrotron Radiation Laboratory, Post Office Box 20450, Stanford CA 94309, USA 

2FYSIKUM, Stockholm University, AlbaNova University Center, S-10691 

When an atom or molecule is adsorbed on a surface new electronic states are formed due to the bonding to the surface. The nature of the surface chemical bond will determine the properties and reactivity of the adsorbed molecule. In the case of physisorption, the bond is rather weak, of the order of 0.3 eV. The overlap of the wave functions of the molecule and the substrate is rather small and no major change in the electronic structure is usually observed. On the contrary, when the interaction energy is substantially higher, there are rearrangements of the valence levels of the molecule, a process often denoted chemisorption. The discrete molecular orbitals interact with the substrate to produce a new set of electronic levels, which are usually broadened and shifted with respect to the gas phase species. In some cases completely new electronic levels emerge which have no resemblance to the original orbitals of the free molecule. 

It is essential to have tools that allow studies of the electronic structure of adsorbates in a molecular orbital picture. In the following, we will demonstrate how we can use X-ray and electron spectroscopies together with Density Functional Theory (DFT) calculations to obtain an understanding of the local electronic structure and chemical bonding of adsorbates on metal surfaces. The goal is to use molecular orbital theory and relate the chemical bond formation to perturbations of the orbital structure of the free molecule. This chapter is complementary to Chapter 4, which 

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Adsorbate Electronic Structure and Bonding on Metal Surfaces Substrate Adatom... 

Nilsson A, Pettersson LGM (2008) Adsorbate Electronic Structure and Bonding on Metal Surfaces, In Nilsson, A, Pettersson LGM, Nprskov JK (eds) Chemical bonding at surfaces and interfaces. Elsevier, Amsterdam 57-142... 

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