On Methyl Formate, Methane, and Deuterated Ammonia in Orion A

Some 25 previously unreported intestellar lines have been detected in the 3--4 mm spectrum of Orion A and are attributed to methyl formate (HCOOCH/sub 3/). A rotational temperature T> or approx. =50 K and a beam-averaged column density Nroughly-equal2(10)/sup 14/ cm/sup -2/ are estimated. A new limit on the abundance of formic acid suggests that (HCOOCH/sub 3/)/(HCOOH)> or approx. =3. Methyl formate transitions at 76.702 and 76.711 GHz, at 85.927 GHz and at 86.224 GHz clearly correspond to previously reported spectral lines attributed to CH/sub 4/, NH/sub 2/D, and (CH/sub 3/)/sub 2/O, respectively. These results suggest that the detections of methane and deuterated ammonia in Orion A should be regarded as tentative only, with important implications for interstellar chemistry and deuterium abundances.