Detection of the Interstellar NH 2 Radical

Abstract

The NH2 radical has been detected for the first time in interstellar clouds. Using the Caltech Submillimeter Observatory, five features containing 15 lines of NH2 have been observed in absorption toward Sgr B2(N) and Sgr B2(M). The NH2 is located in a low-density envelope in front of the dense, hot cores seen in emission lines of other molecules. It is not detected in the hot cores themselves. We infer a NH2 column density of 5 x 10(15) CM-2 , a fractional abundance relative to H-2 of (1-3) x 10(-8), and a total NH2/NH3 column density ratio in the envelope of 0.5. In addition to gas-phase ion-molecule chemistry, shock chemistry is likely to be important. In the dense, hot cores of Sgr B2(M) and (N) the NH2/NH3 ratio is substantially lower, in agreement with significant grain-surface formation of NH but not of NH2.