The fine structure of the (4S°)3p3P term of O I has been determined by interferometric measurement of three triplets at 8446A, 7245A, and 6046A. The term is found to be partially inverted in agreement with Edlén’s findings.
D. O. DAVIS and K. W. MEISSNER, "The Fine Structure of the (4S°)3p 3P Term of Oxygen O I," J. Opt. Soc. Am. 43, 510-511 (1953)