Laboratory study of the O I (7990 Å) branching ratio

Branching ratios for several atomic oxygen 3 p ³ D transitions have been studied. A value of 0.0004 ± 20% for the O I (7990 Å) branching ratio was obtained, which is much smaller than the previously accepted value and in accord with recent calculations and interpretations of the auroral extreme ultraviolet spectra. Measurements of the O I (7002 Å) and O I (11,287 Å) multiplets give branching ratios of 0.05 and 0.10, which are in better accord with calculations. As part of this experiment, results of a study of the highly structured O 2 photoabsorption cross section in the neighborhood of the multiples are also reported.