Compared to the C K-edge spectra, the N and O K-edge XAS and X2PA spectra of pNA are not as rich, a direct consequence of the fewer N and O atoms. The computed N K-edge XAS spectrum, which compares well with the experimental spectrum from Ref. 92, is dominated by the XA 1 → c2B 2 (1s → π * ) transition at 403.7 eV, which is also dominant in the CVS-0 spectrum. This transition is characterized by the a 1 → b 2 orbital transition with the core hole localized on the N atom of the nitro group and a delocalized π * particle orbital (see the raw data in Table and NTO analysis in Table in the SI). The second dominant feature in the XAS transition originates from two transitions, XA 1 → c1B 2 at 402.6 eV and XA 1 → c1B 1 at 402.8 eV. The former is also quite strong in the CVS-0 spectrum and is characterized by the a 1 → b 2 orbital transition with the core hole localized on N atom of the amine group and another delocalized π * particle orbital. In contrast to the XAS and CVS-0 spectra, the CVS-uS spectrum shows different dominant features arising from the XA 1 → c1A 1 and XA 1 → c4A 1 transitions at 401.8 eV and 405.0 eV, respectively. Remarkably, in both these transitions, the core hole is localized on the amine group's N atom and the nitro group does not participate in the particle orbital. The core transitions from the N atom in the nitro group are basically quenched in the XTPA CVS-uS spectrum.