Shakeup processes

The origin of the temperature-independent solid state broadening, 0.4 eV A <0.6 eV we attributed to spatial variations in the electronic contributions to the intramolecular relaxation energies in the vicinity of the surface (18, 19, 22). Similar widths (to 0.6 eV) have been observed in a variety of other contexts, including condensed thin films of and CO molecules ( ) and the sub-monolayer adsorption of these molecules on metal surfaces (29). Interatomic Auger and electron- hole shakeup processes have been proposed, but found to be too small to account for the observed widths in these cases (28, 48). On... 

It should be noted, however, that in actual situations the final states of the shakeup process are molecular Rydberg states and should be described by the MO wave functions. We estimated the contributions from the shakeup probabilities for atoms accompanying A -shell PI to the total (shakeup-plus-shakeoff) probabilities. The shakeup probabilities were calculated with the HS wave functions as the overlap integrals by the method used in our previous work [47]. The shakeup probabilities in PI were found to be about 30 40% of the total probabilities for 3p electrons and about 40 50% for 3d electrons. These large shakeup probabilities suggest that the chemical effect on the shakeup process would be large if the shakeup probabilities are calculated with the MO wave functions and the contributions of the shake process in PI to the Kf3/Ka ratios for 3d elements would be appreciable. 

The main peaks in X-ray Photoelectron Spectroscopy (XPS) for molecules appear because of the photoionization of core electrons. In addition, satellite peaks on the high binding energy side of the main peak have often been observed. These peaks are generally referred to as shakeup satellite peaks. In the sudden approximation, the shakeup process which accompanies photoionization can be considered as a two-step process. First, a core electron is emitted as a photoelectron, creating an inner shell vacancy. In the next step, electron(s) in the same molecule transfer from valence orbital(s) to unoccupied orbital(s) with relaxation of orbital energies. It is important to study these satellites in order to understand the valence and excited states of molecules (1). 

In the present work we tried to interpret the satellite peaks which accompany the CO Cls spectrum as a shakeup process. The values we calculated are used to assign the experimental spectrum. The results are also compared with assignments by other calculation methods. 

In the shakeup process accompanying the inner-shell photoionization, the electrons are excited from occupied orbitals to unoccupied orbitals. In the case of a one-electron shakeup, there are three open shells in the final state. We represent their orbitals as a, b, c, and denote the up-spin electron by -i-, the down-spin electron by -. We can write the determinantal wave function of the final state with open shell structure in the following form (6) ... 

A pair of molecular orbitals involved in the shakeup process produces two states and all the sharp peaks in the experimental spectrum can be assigned to the calculated states. The present and previously reported assignments agree with each other for the first two shakeup excitations due to the Ijt — 2n transition, however the other assignments depend on the theoretical model. The present multiplet calculations are basically performed in the same way as the SW-Xcx method but are in better agreement with the experimental results. One of the improvements was analyzed by considering the exchange Interaction and the atomic constituents of the molecular orbitals concerned. 

Using the total shake (shakeoff plus shakeup) probabilities in Table IV, we modified the the number of 2>p, 3d, and 4s electrons and calculated the K/3IKa ratios after PI. Comparing the K(3IKa ratios for PI with and without the shake processes, the increase in the IKa ratio due to the shake processes is found to be less than 0.5% for V and less than 0.4% for Cr. This fact indicates that the shakeoff and shakeup processes increase the K/3 IK a ratios for PI, but play a minor role in the difference between EC and PI. 

However, for 3p and 3d electrons the final excited states in the shakeup process should be expressed as MO s, while the calculations in Table IV were made for AO s. In order to estimate the contributions of the shakeup process to the total shake probability in Table IV, we calculated the shakeup probabilities accompanying K -shell PI by the use of the method similar to that used in our previous work (36). The shakeup probabilities in PI were obtained to be about 30-40% of the total probability in Table IV for 3p electrons and about 40-50% for 3d electrons. In the shakeup probabilities, the dominant contributions come from the 3p-4p and 3dAd transitions. For V, the former transition amounts to 27% of the total 3p shake probability and the latter is 35% of the total shake probability of 3d... 

The present results suggest that large difference in the K/3 IKa ratios observed in earlier experiments can be ascribed to the combination of the effect of the excess 3d electron in EC and the chemical effect in the samples used in two difference excitation modes. Since in the shakeup process the final excited states should be expressed as a molecular wave functions, it is interesting to calculate the shakeup probabilities by the use of MO s. 

The underlying origin of the multitude of many-body lines in the emission spectrum from quantmn-confined systems is that a recombination is accompanied by shakeup processes whose number increases as the frequency deviates from the Fermi edge. The theoretical value of the dimensionless... 

Figure 11. C 1j XPS spectrum from a PAN-based carbon fiber after potcn-tiostatic polarization at different potentials (vs. SCE) for 20 min in 2.7 M nitric acid solution. The spectra have been fitted with five peaks. Four peaks (G/L mix = 0.5) are separated from the principal fiber carbon peak (at 284.6 eV with G/L mix = 0.8) by 2.0 eV (carbon attached to bridged" oxygen), 3.2 eV (-C=0 carbon), 4.2 eV (-CO2H/R) and 6.1 eV (carbonate/tt- it shakeup processes). The FWHM of the peaks arising from oxidation were at about 2 eV (for polarization potentials 0.5 to 2.0 V) and 1.4 eV (for polarization potentials 2.5 and 3.0 V) (e) and (0- A nonlinear background has been included in the fit. Results of the curve fitting are shown in Table 2. (From Ref. 43.)...

The calculated shakeup-plus-shakeoff probabilities for V and Cr following PI and EC are listed in Table 13. It is clear that the probabilities for EC are negligibly small and those for PI are about 5% for 3p electrons and about 10% for 3d electrons. Using the values of Table 13, we obtained the effective numbers of 3p, 3d, and 4s electrons after EC and PI and calculated the Kjd/Ka ratios for atoms. There is no influence of the shake process on the Kf3/Ka... 

In atoms and molecules, shakeup satellites, corresponding to internal electronic transitions, are routinely observed using photoelectron and resonant Raman spectroscopy. In particular, shakeup satellites can be observed in the two particle spectrum, i.e., when two holes are left in the final state of an atom after electron emission. Satellite s strength can be strongly enhanced in the presence of a resonant intermediate state. For example, in copper atoms, the incident photon can first excite the core 3p electron to the 4s shell the core hole then decays to the 3d shell through the Auger process (with electron ejected from 3d shell) leaving two 3d holes in the final state [48]. For recent reviews of extensive literature the reader is referred to Refe. [49,50]). 

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