Diatomic interhalogens: Systematics and implications of spectroscopic interatomic potentials and curve crossings

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Abstract
Spectroscopically derived potential curves for the low‐lying excited states of the homonuclear and heteronuclear diatomic interhalogens are systematized by taking cognizance of the spin‐orbit state of the dissociation products. Observed regularities lead to the prediction of a bound B (3Π0+) state of F2 with r′e ≃ 1.9 Å, D′e ≃ 3300 cm−1. Several of the heteronuclear interhalogens show evidence of a strong interaction between the B (3Π0+) state and a repulsive Y (O+) state, leading to the formation of a new B′(O+) state. An analysis of these interactions has led to the construction of sets of diabatic potentials consistent with the best estimated adiabatic curves and thus to the determination of the crossing points rx and interaction strengths V12(rx). The patterns of V12(rx) values suggest that they depend mainly upon the spin‐orbit coupling constant of the excited atomic dissociation product. Reported also are repulsive segments of potential curves deduced for the Y (O+) states for a series of 1Π states and a few higher‐lying (Z) states, the latter two series from analysis of existing continuum absorption data. Repulsive interactions in all four families of states studied [3Π0+, 1Π1, Y(O+), and Z] show clear regularities governed by steric effects. Implications of the present results with respect to the theory of interatomic forces, predissociation phenomena, and the scattering of ground state halogen atoms are discussed.