We checked for radiation damage of the samples by measuring either 1 min/short HR-XANES spectrum over the main maximum at the Pu M 4 -edge (Pu 4+ (aq)), 29 spectra or 3 minutes/short spectrum, 8 spectra (Pu 3+ (aq)). The Pu M 4 -edge HR-XANES experiment was performed in the same week as the M 5 -edge HR-XANES experiment of Pu 4+ (aq) but the Pu M 4 -edge data are not discussed herein. No radiation damage was observed for the Pu 4+ (aq) and the Pu 3+ (aq) samples. Note that the M 5 -edge and M 3 -edge HR-XANES/VB-RIXS spectra were measured in the same week for the Pu 4+ and Pu 3+ samples, respectively. The experimental data for the Pu 4+ (aq) and Pu 3+ (aq) samples were collected in different weeks. We assured comparability of the spectra by measuring the same PuO 2 reference in the two different weeks. The respective Pu M 5 edge spectra for the PuO 2 reference is very similar (cf. Figure in SI).