Cross section free-atom

Figure 1. The experimental Cl K-edge absorption cross-section per atom in CI2 (solid lines) compared with theoretical calculations (dashed) based on overlapped free-atom potentials and using the muffin-tin approximation (top) or the full potential (bottom). The theoretical spectra have been shifted by 1.37 eV (top) and 2.80 eV (bottom) to align the first peak.

Polyisobutylene and similar copolymers appear to "pack" well (density of 0.917 g/cm ) (86) and have fractional free volumes of 0.026 (vs 0.071 for polydimethylsiloxane). The efficient packing in PIB is attributed to the unoccupied volume in the system being largely at the intermolecular interfaces, and thus a polymer chain surface phenomenon. The thicker cross section of PIB chains results in less surface area per carbon atom. 

Equation (2.2) is just the Rutherford cross section for scattering of, strictly speaking, free charges. To apply this to atomic electrons that are not free but can be excited4 with energy En, Bohr surmised the sum rule... 

Integration of these component peaks, with appropriate corrections applied for different photoionization cross-sections and inelastic mean free paths, gives the electron populations listed in Table 4. The atomic charges obtained are consistent... 

A quite different aspect of local kinetics is that having to do with changes of charge state, e.g., between H+ and H° or H° and H. Such changes require emission or absorption of electrons or holes. Since the mean free paths of these carriers are large compared with atomic dimensions, it is customary (see for example Lax, 1960) to use a velocity-averaged cross section a as the key descriptor of the rate of a capture reaction such as H+ + e— H°. Explicitly, we write, for this case,... 

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