Resonances resonantly enhanced satellites

Summarizing the individual decay branches of the 4d5/2 -> 6p resonance, one finds that all final ionic states can also be reached by outer-shell photoionization, in (a) and (b) by main processes, and in (c)-(i) by discrete and continuous satellite processes. The effect of the resonance decay will then be a modification of these otherwise undisturbed direct outer-shell photoionization processes which turns out to be an enhancement in the present case. Therefore, these outer-shell satellites are called resonantly enhanced satellites. In this context it is important to note that outer-shell photoionization also populates other satellites, attached, for example, to electron configurations 5s25p4ns and 5s25p4nd. However, the parity of these satellites is even, while the decay branches (c)-(/) lead to odd parity. Therefore, both groups of final ionic states can be treated independently of each other (if configuration interaction in the continuum is neglected). 

Resonance photoemission measurements have been recently made for U metal , and show indeed a resonant enhancement of the satelUte at 2.3 eV only for the threshold energy (5 A i2. hv = 94 eV) (Fig. 15). In addition the main peak at Ep shows the expected off-resonance behaviour. Further support for such an interpretation of the satellite is given by the analysis of the photon excited Auger emission. This is shown to be composed of two different bands also separated by 2.3 eV and due to the two screening channels by 5 f or 6 d states ... 

Fig. 15. Angle-integrated photoelectron energy distribution curves of uranium in the region of the giant 5 d -> 5 f resonance (90 eV < hv < 108 eV). The 5 f intensity at Ep is suppressed by more than a factor of 30 at the 5 ds/2 threshold (see the spectra for hv = 92 and 94 eV) and resonantly enhanced above threshold (see, e.g., the spectrum for hv = 99 e V). At an initial energy 2.3eV below Ep a new satellite structure is observed which is resonantly enhanced at the 5 d5/2 and 5 ds onsets. At threshold the satellite coincides with the Auger electron spectrum, which moves to apparently larger initial energies with increasing photon energy (from Ref. 67)...

Herzberg-Teller Versus Franck-Condon Activity in [Ru(bpy)3]. The vibrational satellite structure resolved in the emission from state 11) is clearly different to the emission structure connceted with state II). This is demonstrated in Fig. 12a,b (cf. also the time-resolved spectra shown in Fig. 16). Several vibrational satellites occur only in the spectrum from state 11) and are not resolved in the state III) emission. Prominent modes with this behavior are found, for example, at 296, 349, 370, 439, 477, 1015, 1569 cm" (see Fig. 12a Table 4). Most of these modes are IR active [212]. On the other hand, a number of dominant modes observed in the emission from state II) (Fig. 12b) are also seen in the state (I) emission (e.g., 158,667,767,1029,1174,1275,1325,1495 cm" see also Table 4). Nearly aU of these vibrations exhibit a Raman activity with strong resonance enhancements, when exciting into the MLCT states [106,211]. 

The earliest of the magnetization transfer experiments is the spin population inversion (SPI) experiment [27]. By selectively irradiating and inverting one of the 13C satellites of a proton resonance, the recorded proton spectrum is correspondingly perturbed and enhanced. Experiments of this type have been successfully utilized to solve complex structural assignments. They also form the basis for 2D-heteronuclear chemical shift correlation experiments that are discussed in more detail later in this chapter. 

Figure 5 Simulated NMR spectra for a nucleus with spin 5/2 (such as Mg) in a single crystal, in the case of (A) and (B) populations corresponding to thermal equilibrium, with non-selective excitation ( hard pulse) in (A) and CT-selective excitation ( soft pulse) in (B). For (C) and (D) populations achieved after saturation of STs, with non-selective excitation (C) and CT-selective excitation (D). For (E) and (F) Populations achieved after complete inversion of the satellite transitions (in the order first, inversion of STl and ST4 and then inversion of ST2 and ST3), with non-selective excitation (E) and CT-selective excitation (F).The numbers at the right-hand side of the spectra in (B), (D) and (F) indicate the corresponding enhancement factors of the CT resonance.

A very effective signal sensitivity enhancement scheme for MQMAS as well as for MAS is the DFS introduced by the group of Kentgens.The underlying principles of DFS and FAM are similar and they have been exphcitly dealt with already. In a nutshell, a cosine amplitude modulated RF carrier wave irradiates the sample at two frequencies, namely, ioq -F w, and aio — Larmor frequency of the spins and is the frequency of modulation. This means that if satellite transitions of a static spins-1 system will be simultaneously... 

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]). 

Possibly one of the most difficult tasks each year is that of writing the General Review of Proton Magnetic Resonance because of the enormous number of papers dealing with such a wide variety of topics. However, I hope the more specialized chapters dealing with specific topics of proton NMR will help to broaden these aspects. The advent of sensitivity enhancement devices has clearly spurred the spectro-scopist to make greater use of carbon-13 satellite spectra. The numerous references, to these satellite spectra, contained in this Volume will undoubtedly encourage chemists to make use of the information contained therein. 

It should be noted, however, that this method does not give a clear-cut answer if the predicted numbers of infrared- and Raman-active fundamentals are similar for various probable structures. Furthermore, a practical difhculty arises in determining the number of fundamentals from the observed spectrum, since the intensities of overtone and combination bands are sometimes comparable to those of fundamentals when they appear as satellite bands of the fundamental. This is panicularly true when overione and combination bands are enhanced anomalously by Fermi resonance (accidental degeneracy). For example, the frequency of the first overtone of the 1/2 vibration of CO2 (667cm ) is very close to that of the > vibration (1337 cm ). Since these two vibrations belong to the same symmetry species ( p, they interact with... 

Xho d sateUit The principal multiplet of the d final state for CuO is known to fall at 12.5 with a smaller one around 10 eV (15). The intensity of the d final state can be enhanced by the Cu 2p 3d resonant excitation process followed by an Auger decay (15). This process is resonant between 72-80 eV. The HTSC s exhibit a similar behavior (j ). The satellites in CuiO and Cu do not have non-resonant components (IS) because the UPS for CuiO and Cu reflect the one-hole DOS. However, the VB XPS of CuO and the HTSC s can and do show a significant nonresonant d satellite (see Figure 1) (23) indeed, it should grow as one approaches the sudden limit. This possibility makes it even more difficult to interpret the XPS data for the HTSC s, since the d satellite at 12.5 in the VB XPS falls at or near the same energy as the Ba spin-orbit split 5p features, which have been very controversial. 

Fig. 10. Valence band spectra from Bi2212 single crystals above and below the Cu 2p resonance. An anomalous enhancement of spectral weight lying between 9 and 13eV binding energy is a satellite feature due to many-body effects.

---