  We report a study on the temperature dependence of the charge-neutral crystal
field (dd) excitations in cupric oxide, using nonresonant inelastic x-ray
scattering (IXS) spectroscopy. Thanks to a very high energy resolution (60
meV), we observe thermal effects on the dd excitation spectrum fine structure
between temperatures of 10-320 K. With an increasing temperature, the spectra
broaden considerably. We assign the temperature dependence of the dd
excitations to the relatively large electron-phonon coupling.
