Electron binding energies measurements

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... 

Fig. 1.57. Electron binding energies measured as VDEs of gas phase negatively charged gold cluster ions in comparison to the reactivity of the same cluster sizes toward molecular oxygen (adapted from [160])...

Obviously hv must be greater than 3- The ejected electron may come from a core level or from the occupied portion of the valence band, but in XPS most attention is focused on electrons in core levels. Since no two elements share the same set of electronic binding energies, measurement of the photoelectron kinetic energies provides an elemental analysis. In addition. Equation (1) indicates that any changes in 3 are reflected in Ek, , which means that changes in the chemical environment of an atom can be followed by monitoring... 

In asymmetric collisions the lowest orbital, the Isa, connects the Is orbital of 2 with the Is of Z. This is illustrated in Fig. 1 for the 35Br-i oZr system. When the system is sufficiently asymmetric the 2pa is far removed from Isa radial coupling between the two is weak and the only way to form a vacancy in the Is shell of the high Z collision partner is by Coulomb ionization from the Isa. Since Coulomb ionization cross sections are dependent on the electron binding energy, measurements of the impact parameter depen-... 

Here, we demonstrate clear and direct evidence for the modified electronic structures of surface Pt atoms in Pt-Co and Pt-Ru by using EC-XPS [Wakisaka et al., 2006]. The sample electrode was transferred between an XPS chamber and an electrochemical (EC) chamber without exposure to air (to minimize contamination of the surface). All photoelectron spectra, including the valence level region) were taken by using a monochromatic Al Ka (hv = 1486.58 eV). The uncertainty of binding energy measurement was less than + 0.03 eV. 

Given the ubiquitous character of molecular orbital concepts in contemporary discourse on electronic structure, ionization energies and electron affinities provide valuable parameters for one-electron models of chemical bonding and spectra. Electron binding energies may be assigned to delocalized molecular orbitals and thereby provide measures of chemical reactivity. Notions of hardness and softness, electronegativity,... 

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 results of a preliminary study of a sample of berkelium oxide (Bk02, Bk203, or a mixture of the two) via X-ray photoelectron spectroscopy (XPS) included measured core- and valence-electron binding energies (162). The valence-band XPS spectrum, which was limited in resolution by photon broadening, was dominated by 5f-electron emission. 

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