Fig. 3. Comparison of simulated and experimental oxygen K-edge NEXAFS spectra from the electronic ground state of (a) malonaldehyde (MA) and (b) acetylacetone (AcAc), as obtained at the CVS-ADC(2)-x/6-311++G** level (unshifted). The underlying NTOs for malonaldehyde are shown as insets. The lowest vertical core-ionization energies are indicated by grey dashed lines. The stick spectra were convolved with a Gaussian line shape (FWHM: 1.0 eV). A broader linewidth than the core-hole lifetime (∼0.15 eV (ref. 101)) was used to represent vibronic effects as to better align with the experiment. (c) The experimental spectrum for gas-phase AcAc was taken from ref. 95 with pre-edge maxima (531.17 and 533.6 eV) and first ionization potential (ref. 99) indicated by red and grey dashed lines, respectively. The experimental pre-edge ratio was estimated (2.0 : 1) by fitting the pre-edge features to Gaussians, using XAS viewer in Larch.¹⁰².