Low-Temperature Emission Spectrum of O2— in Alkali Halides

The fluorescence emission spectrum of the O2— molecule-ion has been measured at 4.2°K in the alkali halides NaF, NaCl, NaBr, KCl, RbCl, KBr, RbBr, and KI. The most intense peaks in the emission spectra are shown to be due to transitions to vibrationally excited levels of the ground state of O2—. The vibrational properties of O2— in its ground state can be represented by an anharmonic oscillator with a vibrational constant (ωe) of approximately 1170 cm—1, and an anharmonicity (ωexe) of 8.5 cm—1. The cause of the fine structure which appears around these intense peaks is not known, but the fine structure for the alkali halides NaF, KCl, and RbBr, which have almost equal anion and cation masses, is quite different from the other alkali halides NaCl, NaBr, KBr, and KI.