9. Results for Hydrogen and Helium
Hydrogen and helium serve as another example or extension
since the general Cromer-Liberman approach did not apply to these
two elements [17-20]. The form is however,
simple, adapted in part from McMaster et al.
. The main difference between the
(plotted) synthesis of Henke et al.
[15,16] and the current form
lies in the range and precision of the computation, the location
of edge energies, the effective number of electrons assumed, and
the interaction with scattering data. In all these respects, the
current tabulation appears superior as a statement of atomic form
However, use of atomic form factors in compounds or solids,
particularly for hydrogen, involves significant shifts and
potential structure not contained in these plots or tables. These
chemical shifts and bonding redistributions serve as a caveat on
use of the lower energy data (unless gaseous atomic hydrogen is
used). Nonetheless, the data is able to represent a good
approximation in general cases.