When comparing the total absorption spectra of Ama + , Ada + , and Ada-CN + in Fig. , we see that the latter two are overall similar (both in their two-peak appearance and the observed vibrational fine structure), while the spectrum of Ama + is quite distinct (three main peaks, no fine structure). For the maxima of the first intense low-energy bands in the spectra, there is a clear trend towards lower excitation energies with the electron-withdrawing ability of the "ligands", with Ama + ∼1.9 eV, Ada + ∼1.8 eV, and Ada-CN + ∼1.2 eV.