Torsionally Excited Methyl Formate in Orion KL

Abstract

We report the first detection of rotational transitions of methyl formate (HCOOCH3) in the first torsionally excited state (vt = 1). Recent progress on the assignment of laboratory spectra of methyl formate made it possible for us to assign about 20 unidentified lines in Orion KL from previous line surveys below 200 GHz to the first torsionally excited methyl formate. The rotational temperature and column density obtained in the first torsionally excited state were 44 ± 10 K and (8.6 ± 3.2) × 1014 cm-2, respectively. They were compared with those in the ground state.