First inflection energies

Examination of Table I reveals that the edge of dibenzothiophene is displaced from that of dibenzyl sulfide, the first inflection energy being some 0.6 eV higher for the former compound. From previous XANES data on dibenzothiophene and dibenzyl sulfide and physical mixtures of the two, it proved possible to identify each compound in the presence of the other (3b,8). Additionally by simply measuring the heights of the third derivative features at 2469.8 eV and 2470.4 eV relative to the base line in the model compound mixtures, a calibration was established which allowed an approximate estimate of the amounts of each component in hydrocarbon samples to be obtained. 

Table I. Sulfur K Edge First Inflection Energies (a)...

Figure 2 XANES comparison of Fe(II) (dashed line) and Fe(III) (dotted line) ammonium sulphate, offset vertically for clarity. First inflection energies for edges occur at about 7123 and 7127eV, respectively. Inset Is — 3d transitions expanded and offset for clarity...

Table 1. Results of XANES, position of edge (first inflection point, energy values are related to a zero point set at 9660.0 eV), (relative absorption at absorption maximum), W (edge width.

The energy calibration was checked by measuring the spectrum of a cobalt foil (thickness 0.0125 mm) with the energy of the first inflection point being defined as the edge energy. 

Detailed studies show that the relaxation time T ib can be calculated from the frequency v found from the inflection point in the dispersion curve, or from the maximum of sound absorption ([192]). For molecules simulated by harmonic oscillators, Tyib is expressed via (Pi,o) by Eq. (8.45). Then, one can ultimately find the transition probability (Pio) or a related quantity Z ib = l/Pi,o which is the number of collisions needed for the deactivation of the first vibrational energy level. 

Sketch a temperature profile that would exist in a one-dimensional laminar flame. Superimpose on this profile a relative plot of what the rate of energy release would be through the flame as well. Below the inflection point in the temperature profile, large amounts of H02 are found. Explain why. If flame was due to a first-order, one-step decomposition reaction, could rate data be obtained directly from the existing temperature profile ... 

The position of an edge denotes the ionization threshold of the absorbing atom. The inflection in the initial absorption rise marks the energy value of the onset of allowed energy levels for the ejected inner electron (216). For a metal this represents the transition of an inner electron into the first empty level of the Fermi distribution (242) and in case of a compound the transition of an inner electron to the first available unoccupied outer level of proper symmetry. Chemical shifts in the absorption-edge position due to chemical combination (reflecting the initial density of states) were first observed by Bergergren (27). 

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