For NH 3 , the XAS spectrum is dominated by the peak at 402.2 eV corresponding to the degenerate XA → c2A and XA → c1A transitions, i.e., the 1s → 3p (XA 1 → cE) transition, with smaller features around 400.5 eV (1s → 3s), 402.8 eV, and 403.5 eV. We refer to Ref. 73 for a more in-depth discussion of the XAS spectrum of NH 3 . On the other hand, both the CVS-0 and CVS-uS X2PA spectra are dominated by the XA → c1A (1s → 3s) transition at 400.5 eV. The 2PA cross section for the XA → c2A transition is, in particular, negligible for the CVS-uS approach. Small features at 402.8 eV and 403.5 eV are also present in the CVS-uS spectrum.