Electron binding energy, determination

A very useful thermodynamic cycle links three important physical properties homolytic bond dissociation energies (BDE), electron affinities (EA), and acidities. It has been used in the gas phase and solution to determine, sometimes with high accuracy, carbon acidities (Scheme 3.6). " For example, the BDE of methane has been established as 104.9 0.1 kcahmol " " and the EA of the methyl radical, 1.8 0.7 kcal/mol, has been determined with high accuracy by photoelectron spectroscopy (PES) on the methyl anion (i.e., electron binding energy measurements). Of course, the ionization potential of the hydrogen atom is well established, 313.6 kcal/ mol, and as a result, a gas-phase acidity (A//acid) of 416.7 0.7 kcal/mol has been... 

Thus we have three possibilities to determine the electron binding energies by means of x-ray excitation ... 

In principle the determination of the electron binding energies EB relative to the Fermi level (cf. Fig. 1) is done be measuring the kinetic energy of the emitted photoelectrons ... 

One of the first tasks of XPS was the precise determination of core electron binding energies for all elements of the periodic table. These data are now tabulated and available for reference (Table 1). On the other hand, there is a great interest in the measurement of the range of low binding energies (0-20 eV) to get a clearer picture about structure and symmetry of the molecular orbitals. 

The primaiy emphasis in this review article is to showcase the use of LEISS to examine the outermost layers of Pt-Co alloys in order to correlate interfacial composition with electrocatalytic reactivity towards oxygen reduction. In some instances, it is desirable to compare the properties of the outermost layer with those of the (near-surface) bulk an example is when it becomes imperative to explain the unique stability the alloyed Co under anodic-oxidation potentials. In such cases. X-ray photoelectron spectroscopy and temperature-programmed desorption may be employed since both methods are also able to generate information on the electronic (binding-energy shift measurements by XPS) and thermochemical (adsorption enthalpy determinations by TPD) properties at the sub-surface. However, an in-depth discourse on these and related aspects was not intended to be part of this review article. 

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