On the effective Zeeman Hamiltonian for a linear molecule in an orbitally degenerate state

Values of the dissociation energies and the interaction constants in the long-range potential

for the B ³Π_Ou+ states of Br₂ and Cl₂ have been obtained from least-squares fits to the attractive part of the Rydberg-Klein-Rees potentials. The term in r ^-6 is not negligible even at large internuclear distances corresponding to the last few vibrational levels. The validity of the long-range inverse-power expansion in the internuclear distance r has been investigated. The expansion is valid outside the electron-overlap region given by

in agreement with the result found in the analysis of I₂.