Choice of Cartesian coordinates employed to represent energy map landscapes projected onto a plane, given in Figures 8 and 9. The molecular geometries of the isolated acetylene and diacetylene are selected. The (X, Y) values report the varying position of the ﹩{{\rm{H}}}^{-}﹩ with respect to the fixed molecular geometry shown in the figure for the acetylene case. They are pictorially defined within the figure.