Core deformation studies by coherent X-ray scattering

'Core' deformation scattering factors have been determined for a series of diatomic molecules. These are defined as the difference between scattering factors calculated from corresponding molecular and atomic core orbital products. The core deformation scattering factors are too small to be measured by current X-ray diffraction methods. The core deformation scattering factors have been expanded in multipolar series about the nuclei. The major component of core deformation is a dipolar term, which is transferable for the same atom in different diatomic molecules. The multipole-expansion terms can be well represented by the Fourier-Bessel transforms of simple density-deformation multipole functions. The dipole density function makes a sizeable contribution to certain molecular physical properties (e.g. electric fields at the nuclei). Even though features of the core density deformation function are also present in the valence molecular orbital products, it is unlikely that total core deformation will be determined by X-ray diffraction measurements. The generalization of these findings to polyatomic systems is discussed.