Torsionally Excited Methyl Formate in Orion KL

Abstract

We report the first detection of rotational transitions of methyl formate (HCOOCH 3) in the first torsionally excited state (v t = 1). Recent progress on assignment of the methyl formate spectra in laboratory made it possible to assign about 20 unidentified lines in Orion KL from previous line surveys below 200 GHz to the first torsionally excited methyl formate. The obtained rotational temperature and the column density in the first torsionally excited state were 44 ± 10 K and (6.9 ± 2.6) × 10 14 cm −2 , respectively. They were compared with those in the ground state.