The Herschbach (Adv. Chem. Phys. 1966, 10, 3 10) classification of XY(-) potential energy curves is updated. Using three independent binary metrics, there are eight (2(3)) curves, expressed in a symmetrical notation as follows: M(m) and D(m), m = 0 to 3, where D and M signify Dissociation and Molecular anion formation in a vertical electron impact, and m is the number of positive metrics. The metrics are the individual adiabatic and vertical electron affinities and the-energy for dissociative electron attachment. Examples are the anions of: H-2 [M(0), D(0)], O-2 [M(2, 1), D(0)], F-2 [D(3,2)], Na-2[M(2); D(1)], and I-2[M(3); D(3,2)]. Improved Morse curves for H-2(-), X-2(-), and O-2(-) are calculated based on more accurate AE(a): F-2, 3.02 +/- 0.01; Cl-2, 2.40 +/- 0.01; Br-2, 2.53 +/- 0.01; I-2, 2.52 +/- 0.005; and O-2, 1.07 +/- 0.07 (all in eV). The AE(a) for the main group homonuclear diatomic molecules are supported by periodic trends.