We report non-resonant x-ray Raman scattering (XRS) measurements from hexagonal boron nitride for transferred momentum from 2 to 9 A˚−1 along directions both in and out of the basal plane. A symmetry-based argument, together with real-space full multiple scattering calculations of the projected density of states in the spherical harmonics basis, reveals that a strong pre-edge feature is a dominantly Y10-type Frenkel exciton with no other \textit{s}-, \textit{p}-, or \textit{d}- components. This conclusion is supported by a second, independent calculation of the \textbf{q}-dependent XRS cross-section based on the Bethe-Salpeter equation.
@article{arxiv.0710.0695,
title = {Exciton spectroscopy of hexagonal boron nitride using non-resonant x-ray Raman scattering},
author = {Yejun Feng and J. A. Soininen and A. L. Ankudinov and J. O. Cross and G. T. Seidler and A. T. Macrander and J. J. Rehr and E. L. Shirley},
journal= {arXiv preprint arXiv:0710.0695},
year = {2009}
}