  We examine the degree of 5f electron localization in URu2Si2 using spin-orbit
sum rule analysis of the U N4,5 (4d \to 5f) edge. When compared to {\alpha}-U
metal, US, USe, and UTe, which have increasing localization of the 5f states,
we find that the 5f states of URu2Si2 are more localized, although not
entirely. Spin-orbit analysis shows that intermediate coupling is the correct
angular momentum coupling mechanism for URu2Si2 when the 5f electron count is
between 2.6 and 2.8. These results have direct ramifications for theoretical
assessment of the hidden order state of URu2Si2, where the degree of
localization of the 5f electrons and their contribution to the Fermi surface
are critical.
