A heavy Rydberg quantum defect analysis of the perturbed D(0u+)ion-pair state of Br2

A quantum defect (delta) analysis, based on the heavy Rydberg model of ion-pair states, is applied to existing data on the D state of Br-2. A linear dependence of the mass-scaled delta on the bound energy is found between 18,000 cm(-1) and at least 22,000 cm(-1) below dissociation, with local vibronic perturbations. At lower bound energies there is an abrupt reversal of the gradient of the energy dependence of delta in the region of strong interaction with the 5p electronic Rydberg states. The energy dependence of delta emphasizes changes in gradient of either the inner or outer wall of the potential. An adiabatic potential energy function for the D state with a modified inner wall is proposed which accounts for the quantum defect in the anomalous region. The highest vibrational levels that were omitted from the standard polynomial fit of the vibrational term values used by previous authors are now included. (C) 2015 Elsevier B.V. All rights reserved.