Excitation ionic

Finally, before turning to a brief review of methodological and theoretical aspects, we mention that one of the distinguishing features of planar conjugated polyene radical cations (cf Section II.D) is that their EA spectra reveal a breakdown of the single-configuration picture for ionic excited states which had been used so successfully in interpreting their PE spectra (cf. Section II). 

Emission spectra of radical cations are obtained by vacuum UV ionization and subsequent laser excitation in noble-gas matrices (see below), or by electron-impact ionization of a beam of neutral parent molecules at energies above the first ionic excited state. After internal conversion to the first excited state, emission may compete more or less successfully with radiationless deactivation. If the experiment is carried out on a supersonic molecular beam one obtains highly resolved emission spectra which, in the case of small molecules, may contain sufficient information to allow a determination of the molecular structure. 

Smith, A.J., Read, F.H. and Imhof, R.E. (1975). Measurement of the lifetimes of ionic excited states using the inelastic electron-photon delayed coincidence technique. J. Phys. B At. Mol. Phys. 8 2869-2879. 

As discussed in Sect. 5, our approximation scheme for the self-energy 2j(E) is designed for a situation where the main ionic excitation strength lies in the continuum. However, from Fig. 2516 it is obvious that this situation is not at hand in Ba because the main ionic excitation strength (in this approximation) has become concentrated to the 4dav(4d 4f P) level. The approximation will then have to be improved in typically two ways ... 

Fig. 28a-h. 4 p self-energy diagrams in a case where a 4d24f ionic excited level dominates the excitation spectrum (see text and compare with Figs. 10, 17-19)... 

Table 3. Energy levels for the ionic excited 4d24t level in atomic Ba in various approximations illustrating the importance of self-consistency in the case of strongly localized levels...

Im. Z i(E) can be considered as a product of an ionic excitation density of states and an energy-dependent coupling constant. In model calculations one can independently vary the shape and the band with of the denstiy of states and the strength of the coupling constant. In the present case we can only vary these parameters indirectly by changing the atomic number Z. Since the self-energy involves the polarizability of the ionic system there must be an oscillator-strength sum rule such that... 

In the actual calculation94, 95) no attempt was made to include the detailed level structure. The 5 pfod ionic excitations were approximated by 5 pav (5 pmd P RPAE) (cf. Sect. 6.1) and the potential was based on the frozen ground-state orbitals. The resulting spectral strength distribution is given in Fig. 32 a. The shift of the 5 s.i/2 core level of 2.5 eV is of the right order but somewhat too small. Inclusion of the dipole polarizability of the 4d-shell through... 

Before we proceed to discuss the valence spectrum in greater detail, it is very instructive first to consider the Is deep core level spectrum, which is not complicated by the presence of several overlapping satellite spectra and therefore gives direct information about the ionic excitation level structure. If the core level spectrum is experimentally available, this may then be of great help for interpreting valence level spectra. 

In Figs. 42b, c the ionic excited states have the full molecular symmetry and by including diagonal hole-hole and hole-electron ladders in analogy with Figs. 42d,e will... 

Fig. 48. Experimental valence level ESCA spectrum for C0124). Ionic excitation levels (top of picture) inferred from the core hole spectrum in Fig. 47...

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