We attribute this to an inability of CC2 to properly account for relaxation effects, probably because of the lack of double excitations in the excitation manifold, along with the more approximate treatment of ground state correlation. In the gas phase, CC2 has earlier been shown to yield compressed XA spectra. Having established the unreliability of CC2, we then focused on the performance of CCSD, both with respect to experiment and with respect to the results of previous calculations based on TP-DFT. In Figures and we thus compared the XA spectra obtained, at the PE-CCSD/6-311++G** level, for four different snapshot structures of each species, together with their total averaged spectra and the experimental spectra. Despite the differences between the spectra of the four snapshots, one clear picture emerges: in the case of ammonium, CCSD yields significant intensity in the post-edge region, in agreement with the experimental profile.