Inner valence states, double

The calculations were performed using a double-zeta basis set with addition of a polarization function and lead to the results reported in Table 5. The notation used for each state is of typical hole-particle form, an asterisc being added to an orbital (or shell) containing a hole, a number (1) to one into which an electron is promoted. In the same Table we show also the frequently used Tetter symbolism in which K indicates an inner-shell hole, L a hole in the valence shell, and e represents an excited electron. The more commonly observed ionization processes in the Auger spectra of N2 are of the type K—LL (a normal process, core-hole state <-> double-hole state ) ... 

These spectra have already been used in section 2.12 as examples of the extended alkali model. They correspond to the excitation scheme d10 2 1So — d9 2np,nf(J = 1), where 2 are the valence electrons. Double excitations have also been investigated, especially in Zn [344] and are very significantly enhanced as they approach an inner-shell excited transition. This shows that final state mixing is the dominant mechanism for double excitation. 

The prototypical indirect double photoionization process is the classical Auger effect, where the single-hole state created by ejection of an inner-shell electron exists for a significant time before ejection of a second electron. Alternatively, an intermediate singly charged state may exist as a multiply excited valence state or a Rydberg state, but whatever its nature, a lifetime of at least a few femtoseconds will normally allow the whole process to be considered as a sequence of two distinct steps. A sharp peak in the photoelectron spectrum and also, therefore, in... 

Figure 21. The inner valence Auger effect in formaldehyde (methanal). The broad peak in the regular photoelectron spectrum near 34 eV is an inner valence (IV) band based on C2s ] ionization. It recurs as a peak in the electron distribution for double photoionization and in the quantum yield. The uppermost curve shows the spectrum of HCH02+, where the ground state is strongly populated by this effect. 

Concerning the role of dimensionality we observed, in the three fully passivated cases, that the material is a semiconductor, as the band structure of the Si[i]-SiC>2 SL in Figure 39(a) shows, and that there is an opening of the gap as the thickness of the Si layer decreases. The band structure shows a gap which is slightly indirect for the presence of a state at the top of the valence band (mostly related to the Si atoms in the inner Si layer), that is partially due to the interaction between the interface Si and its double-bonded O atom. If we remove this extra O, leaving the two dangling bonds of the interface Si unsaturated, we find that the material is still a semiconductor with a new... 

The availability of a complete range of photon energies from storage ring synchrotron emission has allowed the formation and decay of some exotic inner-shell hole states to be studied. The formation of double core-hole states, where two electrons are removed from the same inner shell by direct photoionization is expected to be weaker by several orders of magnitude than the formation of doubly charged ions with two vacancies in the valence shell... 

Another unusual type of highly excited doubly charged ion has one hole in a deep inner shell and one in the valence shell. Such states are of interest theoretically because of (a) the presence of distinct electron vacancies and (b) several possible pathways for their production [86]. The first observation of direct formation of such states in Ne and N2 was recently achieved by the magnetic bottle TOF method [87]. The cross section for their formation is very low, and the electron distribution in the Ne case shows both a direct contribution and an indirect pathway. For the final states from s l2p l ionization the intermediate states are satellites of the Islsi1 3S)ns series whose lines show asymmetric Fano profiles. The presence of these profiles demonstrates that the matrix elements representing direct double ionization, formation of the intermediate states, and interaction of those states with the continuum are of similar magnitudes. 

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