Characterization of homonuclear diatomic ions by semiempirical morse potential energy curves .1. The halogen anions

Morse potential energy curves for the homonuclear diatomic halogen anions and their excited states were constructed using experimental data available from the literature. All of the curves are uniquely or overdetermined. The properties of the negative ions have been related to those of the neutral by using three dimensionless parameters, k(A), k(B), and k(R), to modify the Morse curves of the neutral. The magnitudes of the parameters are reasonably consistent and suggest ranges for other homonuclear diatomic ions. A set of Morse potential energy curves is predicted for astatine anions on the basis of the consistency of these parameters. These curves are a significant improvement over those presented 10 years ago because of the existence of additional experimental data. In cases where the curves are overdetermined, these data agree very well with the calculated Morse potentials. Estimates for internuclear distances were made on the basis of the assumption of the additivity of radii. Agreement with available experimental data which were used to define the curves shows this assumption to be valid. The bond dissociation energies of the ground states of the halogen anions agree with those of the corresponding isoelectronic rare gas positive ions within the experimental error. This led to the use of the experimental values for the excited state bond dissociation energies of the rare gas positive ions to estimate those for the corresponding state of the halogen negative ions. Experimental cross-section data have been used to define Morse potentials for the higher spin orbital substates of iodine which were previously only estimated. However, the structure in the cross-section data and a recently published theoretical calculation has led to the conclusion that I-2(-) may consist of more than the currently projected six states. In addition, the spin orbital substates of F-2(-) are now better defined.