DETECTION OF NITRIC-OXIDE IN THE DARK CLOUD L134N

We report the first detection of interstellar nitric oxide (NO) in a cold dark cloud, L134N. Nitric oxide was observed by means of its two 2Π1/2, J = 3/2 → 1/2, rotational transitions at 150.2 and 150.5 GHz, which occur because of Λ-doubling. The inferred column density for L134N is NNO ∼ 5 × 1014 cm-2 toward the SO peak in that cloud. This value corresponds to a fractional abundance relative to molecular hydrogen of fN0 ∼ 6 × 10-8 and is in good agreement with predictions of quiescent cloud ion-molecule chemistry. NO was not detected toward the dark cloud TMC-1 at an upper limit of fNO ≤ 3 ×10-8.