Excitation energies of barium oxide bands measured in flames

Abstract

Experiments are described that yield additional information about the excitation energy of visible barium oxide bands appearing in flames. Excitation energy differences are derived directly from the ratios of thermal band intensities as a function of temperature and agree with the value calculated from the known (relative) energy-level diagram. Absolute excitation energies are derived from the temperature dependence of the ratio of band-to-line intensity under thermal equilibrium conditions and under the assumption of a most probable value for the dissociation energy of BaO. Flames with temperatures ranging from 1911 to 2886 K were used. The excitation energy values found can be reconciled with the assumption that the lower 1∑ state of the optical transitions is the electronic ground state only if there are low-lying electronic levels that contribute at least a factor of 6 to the electronic partition function.