Bond strengths, transition metal electronic applications

In the following, we will discuss a number of different adsorption systems that have been studied in particular using X-ray emission spectroscopy and valence band photoelectron spectroscopy coupled with DFT calculations. The systems are presented with a goal to obtain an overview of different interactions of adsorbates on surfaces. The main focus will be on bonding to transition metal surfaces, which is of relevance in many different applications in catalysis and electrochemistry. We have classified the interactions into five different groups with decreasing adsorption bond strength (1) radical chemisorption with a broken electron pair that is directly accessible for bond formation (2) interactions with unsaturated it electrons in diatomic molecules (3) interactions with unsaturated it electrons in hydrocarbons ... 

In Table 3 we compare the bond strengths for Cl2Ti=X and H2C=X as a function of electron correlation. For double bonds, the differential correlation error between H2C=X and Cl2Ti=X systems is between about 30 and 40 kcal/mol. Clearly, while HF may be acceptable for some organic applications (at least as a reference configuration for standard Cl calculations), it is totally unacceptable for transition metal systems. 

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