Notes

¹The energy E and wavelength of light are related by the expression E = hc/, where h is the Planck constant and c is the speed of light. Macromolecular crystallographers traditionally characterize X-rays in terms of their wavelength in Å. On the other hand, scattering factors are commonly tabulated as a function of energy in eV or keV. Moreover, because of the inverse relationship between E and , fixed increments or intervals of energy will have very different values in Å over the full spectrum, making it inconvenient to use wavelengths on these occasions. Therefore, in some instances throughout this paper energy units will be used when convenient, although most of the discussion will be in terms of wavelength. The formula = 12398/E can be used to translate the energy in eV to the corresponding wavelength in Å.

²This statement refers to K and L_II and L_III absorption edges edges. L_I edges are less useful for MAD experiments, because the typical value of at the inflection point is only about -9  e^-, compared with approximately -19 and -12  e^- for the L_III and L_II absorption edges, respectively (in the presence of a white line, becomes even more negative at these edges). The smaller || at the edge results in smaller dispersive differences.