TIMASSS: The IRAS16293-2422 millimeter and submillimeter spectral survey: Tentative detection of deuterated methyl formate (DCOOCH3)

Abstract

Context. High deuterium fractionation is observed in various types of environments such as prestellar cores, hot cores, and hot corinos. It has proven to be an efficient probe for studying the physical and chemical conditions of these environments. The study of the deuteration of different molecules helps us to understand their formation. This is especially interesting for complex molecules like methanol and bigger molecules for which it may allow differentiation of gas-phase and solid-state formation pathways. Aims. Methanol exhibits a high deuterium fractionation in hot corinos. Since CH3OH is thought to be a precursor of methyl formate we expect that deuterated methyl formate is produced in such environments. We searched for the singly-deuterated isotopologue of methyl formate, DCOOCH3, in IRAS 16293-2422, a hot corino well-known for its high degree of methanol deuteration. Methods. We used the IRAM/JCMT unbiased spectral survey of IRAS 16293-2422, which allowed us to search for the DCOOCH3 rotational transitions within the survey spectral range (80-280 GHz, 328-366 GHz). The expected emission of deuterated methyl formate is modelled at LTE and compared with the observations. Results. We have tentatively detected DCOOCH3 in the protostar IRAS 16293-2422. We assign eight lines detected in the IRAM survey to DCOOCH3. Three of these lines are affected by blending problems, and one is affected by calibration uncertainties; nevertheless, the LTE emission model is compatible with the observations. A simple LTE modelling of the two cores in IRAS 16293-2422, based on a previous interferometric study of HCOOCH3, allows us to estimate the amount of DCOOCH3 in IRAS 16293-2422. Adopting an excitation temperature of 100 K and a source size of 2" and 1$\farcs$5 for the A and B cores, respectively, we find that NA, DCOOCH3 = NB, DCOOCH3 ∼6 × 1014 cm-2. The derived deuterium fractionation is ∼15%, consistent with values for other deuterated species in this source and much greater than expected from the deuterium cosmic abundance. Conclusions. If its tentative detection is confirmed, DCOOCH3 should now be considered in theoretical models that study complex molecule formation and their deuteration mechanisms. Experimental work is also needed to investigate the different chemical routes leading to the formation of deuterated methyl formate. © ESO, 2010.