Atomic Oxygen Fine-Structure Splittings with Tunable Far-Infrared Spectroscopy

We have accurately measured fine-structure splittings of atomic oxygen (l60) in the ground state using a tunable far-infrared spectrometer. The 3P,-3P, splitting is 2,060,069.09 (10) MHz, and the 3P1-3P2 splitting is 4,744,777.49 (16) MHz. These frequencies are important for measuring atomic oxygen concentration in Earth's atmosphere and the interstellar medium. Subject headings: infrared: spectra - interstellar: matter - laboratory spectra - planets: atmospheres