J.G. Dojahn et al. (J. Phys. Chem. 100, 9649 (1996)) characterized the potential energy curves of the

Question:

J.G. Dojahn et al. (J. Phys. Chem. 100, 9649 (1996)) characterized the potential energy curves of the ground and electronic states of homonuclear diatomic halogen anions. These anions have a ²Σ_u⁺ ground state and ²Π_g, ²Π_u, and ²Σ_g⁺ excited states. To which of the excited states are electric-dipole transitions allowed? Explain your conclusion.