Partial yielding

The reaction sequence (steps) of a synthesis may be linear (i) or convergent (ii) [16]. Because the total yield Y of a synthesis is the product of the partial yields y,... 

The most satisfactory method, which can also be used to prepare gram quantities, is to heat the vacuum-dried hydrous oxide in a sealed, evacuated Pyrex reaction vessel with thionyl chloride vapor at 350°-500°C, the volatile, yellow pentachloride (m.p. 306°C) being obtained in better than 95% yield (47). Thermal decomposition of SO(PaCl6)2 is less satisfactory (15) and only gives a partial yield of the pentachloride, leaving an unidentified black residue. 

Partial yield measurements have been carried out by Stohr for O2 on Ni(lOO) and Si(ll 1) and for oxidized Al. The results for Ni(lOO) with a monolayer of oxygen (40 Langmuir exposure) are shown in Figure 17. At this coverage O atoms... 

Hi) Auger partial yield. The transition time in Auger emission is of the order of 10 —10" s, which is similar to the average time for a photoelectron in the energy... 

The partial yield of atomic species A and B is defined by v Number of Ejected Atoms A, B... 

The partial sputtering yield, TA, of species A is proportional to the surface concentration, NA, and similarly YH is proportional to NSB. The ratio of partial yields is given by... 

When steady state conditions have been achieved, conservation of mass requires that the ratio of partial yields equals the bulk concentration ratio... 

In spite of their similarity potassium hydroxide and sodium hydroxide differ in their effects. Potassium benzenesulfonate and potassium hydroxide give an almost quantitative yield of phenol, but only a partial yield is obtained in sodium hydroxide. This relationship is, however, reversed when one tries to convert benzenetrisulfonic acid into phloroglucinol with potassium hydroxide... 

The partial yield of electrons in an energy window AE at a fixed final state energy E, as a function of photon energy, where E is fixed at < 5eV so that only secondary electrons are measured, is referred to as partial yield spectroscopy. When E > 5eV, although the technique is experimentally identical, it is used to study initial state and excitonic effects and is known as constant final state spectroscopy. 

Constant initial state techniques require the photon energy and electron energy analyser to be scanned synchronously so that hv — E is kept constant. In this way, the photon energy dependent partial yield of electrons in an energy window AE at a fixed initial state energy E = E — hv is measured. Core level to empty surface state transitions are enhanced by selecting the appropriate E corresponding to a minimum in the valence band emission. 

The mass spectrometric method of fission product yield measurements can be applied to the entire mass range of fission products. Inghram et al. (55) investigated fission products in the rare earth region and showed how the partial yield curves obtained from isotope abundance measurements for the various elements can be fitted together by the method of stable... 

The optical spectrum df/dE, and the derived excitation (14) spectrum (1/E) (df/dE) are thus seen to be the most important characteristics of a molecule even from the point of view of its radiolytic properties. By integrating the differential yields given by Equation 3 over relevant parts of molecular spectra we can, of course, obtain the partial yields for particular types of transitions—e.g., the yields of all excitations, ionizations, etc., as well as the total yield of all primary optical transitions ... 

An extremely important issue for the Co EMS methodology is the study of aftereffects of the Co —> Fe radioactive decay process. For a complicated biocomplex, for example an enzyme, especially with more than one cationbinding site (n> I) at the active center, each of the parent Co" chemical species (with its own coordination microenvironment) would, in principle, give its own yield of the aliovalent Fe " form (as a result of aftereffects). It is often the case when such daughter Fe " lines in the source experiment have very close parameters and, being also relatively broad, virtually do not resolve in the spectrum and thus have to be fitted with a single doublet. Since the partial yields for the n aliovalent Fe " forms remain unknown, the real distribution of Co" between the n sites in the sample under study is therefore also unknown, even when the corresponding n lines for Fe" do resolve and can easily be quantitatively assessed. 

Fig. 8 Schematic representation of partial yield photoemission spectroscopy.

GERISCHER The vacant surface states can be detected in the partial yield spectroscopy because the matrix element for an electronic transition from the core states to these surfaces states is large since they are concentrated at the same atom. What is the chance to observe an optical transition between occupied and vacant surface states ... 

SXE can also be excited by photons (fig. 4a), in which case the thickness of the investigated surface depth is increased by a few orders of magnitude. Conventional SXA of thin samples has in practice no surface sensitivity when compared to the other methods. The detection of the photon absorption can also be performed by measuring the yield of the emitted electrons so that the surface sensitivity may even be very high if the electrons are selected in a narrow energy window at low kinetic energy (partial yield spectroscopy). 

Fig. 19. Partial yield spectra of C p3> y-Ce and o-Ce in the region of the 4d-4f excitation measured with electrons having 4eV kinetic ener (Wieliczka et al. 1982). The vertical lines are for some of the prominent multiplet final states as in fig. 7.

---