Ionization peaks

As discussed in Chapter 1, the development of PES showed that the spectra could be simply interpreted if one assumed that electrons occupy delocalized molecular orbitals (25,26). In contrast, VB theory, which uses localized bond orbitals (LBOs), seems completely useless for interpretation of PES. Additionally, since VB theory describes equivalent electron pairs that occupy LBOs, the experimental PES results seem to be in discord with this theory. An iconic example of this failure of VB theory is the PES of methane that displays two different ionization peaks. These peaks correspond to the a and t2 MOs, but not to the four equivalent C—H LBOs in Pauling s hybridization theory. 

Fig. 5.5-2. The Franck-Condon analysis of the 5 ionization peak for Mo2(02CCH3)4, showing how the Mo-Mo bond length change is estimated. By permission from Ref. 172...

Conformational analysis of 1,4,7-trithiacyclononane 10 in the gas phase was done using ab initio molecular orbital calculations at the HF and MP2 levels as well as microwave and photoelectron spectroscopies. The photoelectron spectroscopic data showed evidence for at least two conformations with different ionization energies. Using the calculated photoelectron spectra, the observed sulfur 3p-ionization peaks can be assigned to Cj and U2 conformations. Forty of the observed microwave transitions can be assigned to a Cj symmetry, while additional microwave lines are believed to be due to a nonrigid U2-symmetry conformation <1997PCA9180>. 

A most important aspect of these data is the temperature dependence of the width of the molecular soli ph to-ionization peak. Xhis X-dependence is of the form A (X) = A + c X, which... 

Figures 5-8 show further that the two features of the condensed phase spectra which differ from their gas-phase counterparts are the energies and widths of the individual ionization peaks or optical-absorption lines. In both the UPS and UAS spectra the lines in the solid state are shifted to lower energies relative to the corresponding ones in the gas phase by a relaxation energy, 1 eV for ion states and % 0.1 eV for exciton states, associated with the intermolecular polarization induced by the ion or exciton (1, 2, ). In addition, these...

We summarize here the features of the UPS and UVA data which lead to the molecular ion concept for these aromatic pendant group polymers. First, the spectra of the polymers PVP and PS are essentially identical to those of condensed model molecular moieties 2-vinyl pyridine and ethyl benzene, respectively. Second, the solid-state spectra are related to the gas-phase spectra of these model moieties by an essentially constant shift to higher energy (lower binding energy) of all the ionization peaks by = 1.5 0.1 eV. Third, the width in energy of the solid-state ionization peak is Air = 1.0 0.1 for both polymers... 

The three switches defined above rest on the mechanism of interspersed resonances, which was first suggested theoretically by Howard (1991). In the following we demonstrate the action of such a switch in the case of bichromatically driven hydrogen Rydberg atoms. It results in the prediction of a new kind of ionization peak in the microwave ionization of hydrogen Rydberg atoms. Recently performed experiments indicate that the effect actually exists. 

Figure 2 also shows a d-band, arising from the four nickel atoms with d electrons explicitly included, extending downward from about -0.5 a.u. for the clean surface, adsorbed CH and coadsorbed CH and H cases. In a Ni atom, for this basis, the average d orbital energy is -0.44 a.u., a value close to the Hartree-Fock result. Photoemission measurements position the d ionization peaks of nickel near the Fermi level, a result also obtained by most density functional treatments of nickel clusters. Application of Koopmans theorem would therefore suggest that the present d-ionization... 

FIGURE 1.1.2 (Top) DFT/B3LYP simulation (dashed lines) of the vibrational structure of the UPS first ionization peak of pentacene (solid lines) and (bottom) computed Huang-Rhys factors as a function of the frequency. The normal modes of the cation species with the largest Huang-Rhys factors ((10 modes) have been used for the simulations. A scaling factor of 0.9613 has been applied to the computed frequencies. The transition intensities were convoluted with Lorentzian functions with full-width at half-maximum (FWHM) of 0.060 eV. The HOMO wavefunctions obtained at the DFT/B3LYP level is also illustrated. 

The final expression for the total cross section for Xth ionization peak is given by ... 

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