  We investigate the behavior of a $d$-$d$ transition in NiO using a new x-ray
spectrometer with 0.025 eV resolution at 15816 eV, and via ab-initio ligand
field theory calculations. The transition at ~1.7 eV energy transfer is
measured at temperatures between 20 and 800 K, at a momentum transfer
|$\bf{Q}$| = 6.52 \AA$^{-1}$. Fine structure is clearly observed at 20 K. As
temperature is increased, the excitation shifts to lower energy and broadens.
We explain the energy shift as being related to thermal expansion and to
magnetism. The broadening is well fit considering thermal fluctuations of the
Ni-O bond length, with a scale factor found to be in reasonable agreement with
calculation.
