Neutral 3d excitations in insulating VO2 as seen with resonant inelastic x-ray scattering at the V L3,2 edges

We present resonant inelastic x-ray scattering (RIXS) results on insulating monoclinic VO2 with excitation across the L-2,L-3 edges of vanadium. The spectra measured near threshold in the L-3 region and in the L-2 region show a Raman behavior with a clear peak around 0.9 eV transferred energy. The analysis of the data allows the neutral excitation spectrum of the system up to about 2-2.5 eV to be determined. These excitations are due to dd transitions, whose main contributions are discussed. The possibility of {d(1);d(1)-> d(2);d(0)} charge fluctuations within a dimer in RIXS is also discussed. The results are compared with available information on optical constants and on electron energy loss spectroscopy. Due to the low symmetry of the system, there is a similarity between the Raman spectrum obtained with RIXS and the optical absorption spectrum.