ROTATIONAL SPECTRUM AND TENTATIVE DETECTION OF DCOOCH₃-METHYL FORMATE IN ORION

Abstract

New centimeter-wave (7–80 GHz) and submillimeter-wave (580–661 GHz) spectra of a deuterated species of
\nmethyl formate (DCOOCH3) have been measured. Transitions with a maximum value of J = 64 and K = 36 have
\nbeen assigned and fitted together with previous measurements. The internal rotation of this compound was treated
\nusing the so-called rho axis method. A total of 1703 transitions were fitted using this method. Only 24 parameters
\nwere employed in the final fit, which has an rms deviation of 94.2 kHz. The dipole moment and the nuclear
\nquadrupole coupling constants of the deuterated specie have also been obtained. This new study has permitted a
\ntentative detection of DCOOCH3 in Orion with the IRAM 30 m telescope based on the observation of more than
\n100 spectral features with low blending effects among the 400 lines expected in the observed frequency domain (for
\nwhich over 300 are heavily blended with other species). These 100 transitions are above noise and confusion limited
\nwithout heavy blending and cannot be assigned to any other species. Moreover, none of the strongest unblended
\ntransitions is missing. The derived source-averaged total column density for DCOOCH3 is 7.8 × 1014 cm−2
\nand theDCOOCH3/HCOOCH3 column density ratio varies between 0.02 and 0.06 in the different cloud components
\nof Orion. This value is consistent with the deuteration enhancement found for other species in this cloud.