Supplementary Material

The supplementary material includes a direct comparison of band B with band X/A in the PE spectrum of Sm3O-, a simulation of band B assuming a 460 cm-1 vibrational progression, plots of asymmetry parameters of all experimental spectra, plots of spectral simulations based on computed ADE/VDE values for several states of Ce3O-, Sm3O- and Gd3O-, and tables of computational results that include vibrational frequencies.