Computed pseudo-2D RPES for the ﹩{{\rm{H}}}^{-}+\mathrm{HCCH}﹩ reaction for the collinear approach (﹩\vartheta ={180}^{{\rm{o}}}﹩) of the ﹩{{\rm{H}}}^{-}﹩ reagent to the ﹩{\mathrm{HC}}_{2}{\rm{H}}﹩ partner.The angle's definition is reported in Figure 1 and also in the main text. The corresponding minimum energy path (MEP) is shown by a red line on the energy map, going from reactants to products.