Detection of the Interstellar NH 2 Radical

The NH 2 radical has been detected for the first time in interstellar clouds. Using the Caltech Submillimeter Observatory, five features containing 15 lines of NH 2 have been observed in absorption toward Sgr B2(N) and Sgr B2(M). The NH 2 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 NH 2 column density of 5×10 15 cm −2 , a fractional abundance relative to H 2 of (1-3)×10 −8 , and a total NH 2 /NH 3 column density ratio in the envelope of 0.5