On methyl formate, methane, and deuterated ammonia in Orion A

Some 25 previously unreported interstellar lines have been detected in the 3-4 mm spectrum of Orion A and are attributed to methyl formate (HCOOCH3). A rotational temperature of about 50 K and a beam-averaged column density of about 2 x 10 to the 14th per sq cm are estimated. A new limit on the abundance of formic acid suggests that HCOOCH3/HCOOH is not less than 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 CH4, NH2D, and (CH3)2O, 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.