Phase change on scattering

FIGURE 14.17. Phase change on anomalous scattering. Compare this Figure with Figure 3.8 (Chapter 3). (a) Normal, and (b) anomalous scattering. 

The calculations showed [54,55] significant effect of the GP on scattering angle resolved cross-sections for a particular final rotational state. It is interesting to see the change of these distributions due to the geometric phase... 

At a fundamental level, it has been shown that PECD stems from interference between electric dipole operator matrix elements of adjacent continuum f values, and that consequently the chiral parameters depend on the sine rather than the cosine of the relative scattering phases. Generally, this provides a unique probe of the photoionization dynamics in chiral species. More than that, this sine dependence invests the hj parameter with a greatly enhanced response to small changes in scattering phase, and it is believed that this accounts for an extraordinary sensitivity to small conformational changes, or indeed to molecular substitutions, that have only a minimal impact on the other photoionization parameters. 

The above argument assumes that the intrinsic phase change of each wave on being scattered by atoms W and Y is the same and thus can be ignored. This assumption holds in the case of normal scattering, that is, if the frequency of the incident radiation is much greater than the critical absorption frequencies of the irradiated atoms. When, however, the incident wavelength is a little shorter... 

X-ray diffraction [72], often in combination with DSC or NMR, is another useful tool for the study of drug-membrane interactions. It is especially useful to obtain information on the localization of drag molecules and on the conformational (phase) changes of membranes. The method is based on comparing the electron density profile of membranes to which drug has or has not been added. If partially hydrated probes are used, coherent Bragg-like scattering is obtained at reasonable resolution. 

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