Shake-up spectra

The OVGF function method provides a quantitative account of ionisation phenomena when the independent-particle picture of ionisation holds and as such is most applicable in the treatment of outer-valence orbitals. It provides an average absolute error for vertical ionisation energies below 20 eV of 0.25 eV for closed shell molecules. The TDA and ADC(3) methods allow for the breakdown of one particle picture of ionisation and so enable the calculation of the shake up spectra. The ADC(3) is correct up to 3rd order, is size consistent and includes correlation effects in both the initial and final states. 

The core ionization of an atom stabilizes all the valence electrons in the atom. Depending on whether the electronic transition shifts electron density to or from an atom, the energy separation for a shake-up peak of that atom will be less than or greater than the energy of the neutral molecule ionization81. As an illustration of these effects, let us consider the shake-up spectra of formamide, H2NCH082. The principal transitions involved are the vl - n3 and 7r2 - 7r3 transitions. The tTj... 

Nilsson A, TiUborg H, Martensson N (1991) Electronic structure of adsorbates from core level shake-up spectra CO and N2 on Ni(lOO). Phys Rev Lett 67 1015... 

The present review has presented some illustrations of the CASSCF method. The method has been applied to a number of problems not considered here. Core ionization and shake-up spectra have been successfully analysed in terms of near-degeneracy effects in the ionized states. The shake-up spectra of p-nitroaniline ° and p-aminobenzonitrile ° highlight this type of application. Studies of valence ionization spectra have been done for ozoneand acetylene s . 

Figure 3.9. Fxperimenlal Cls and Nls shake-up spectra of DPPDA (all -NH- structure) and DPQDl (all =N-structure). (Reprinted with permission from ref. 101, Am. Inst, Phys.)...

XPS CIs shake-up spectra of the AI/DP7 interface for increasing Al coverage, from the pristine system (bottom curve) to approximately five monolayers (top spectnim). 

It is possible to obtain useful information about the valence iT-electronic structure of a molecular ion through shake-up structures in XPS spectra, appearing as weak satellites on the low binding-energy side of the main line. The shake-up structure reflects the spectrum of the l-electron-2-hole states generated in connection with photoionization processes, and can sometimes be used as linger prints of certain molecular constituents by comparison with shake-up spectra of known systems. 

The capping phenyl groups on the diphenylpolyenes enhance the environmental stability with respect to the unsubstituted polyene molecules. Since the phenyl groups do not contribute significantly to the first few frontier orbitals, the diphenylpolyenes are suitable as models for short polyenes [64-66] the separation of the frontier orbitals in terms of polyene- and phenyl-dominated molecular orbitals can be deduced from a comparison between experimental UPS spectra and theoretical quantum-chemical calculations as well as from experimental fingerprints in the XPS C(l,s) core-level shake-up spectra, as demonstrated below for a diphenylpolyene with seven carbon-carbon double bonds in the polyene part of the molecule, i.e., a.w-diphenylletradecahep-taene (DP7) [66]. The chemical structures of the diphenylpolyenes are displayed in Fig. 23.2. 

NIL Nilsson, A., Martensson, N. Core-level shake-up spectra from ordered C,N and O overlayers on Ni (100) Chem. Phys. Lett. 182 (1991) 147. 

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