ATOMIC OXYGEN IN MOLECULAR CLOUDS - HIGH-RESOLUTION SPECTROSCOPY OF THE [O-I] 63-MICRON LINE TOWARD DR-21

We report the first high-resolution spectra of the [O I] 63 mu m fine- structure line toward DR 21. The observations were made from NASA's Ku iper Airborne Observatory using the MPE/UCB imaging spectrometer FIFI. The spectra show a pronounced dip, which may be due to absorption by a foreground molecular cloud, seen against the broad [O I] emission fr om DR 21. In this case we derive a column density of cold, atomic oxyg en of greater than or similar to 5 x 10(18) cm(-2), corresponding to a relative abundance of atomic oxygen of [O]/[H] greater than or simila r to 6 x 10(-4). Therefore, most of the gas-phase oxygen in this cloud would be in atomic form. This result is in contrast to predictions by common chemistry models for a steady state cloud and may support mode ls which predict a high abundance of atomic oxygen in dark cores of mo lecular clouds.