2013A&A...552A.117R

Dimethyl ether is one of the most abundant complex organic molecules (COMs) in star-forming regions. Like other COMs, its formation process is not yet clearly established, but the relative abundances of its deuterated isotopomers may provide crucial hints in studying its chemistry and tracing the source history. The mono-deuterated species (CH₂DOCH₃) is still a relatively light molecule compared to other COMs. Its spectrum is the most intense in the THz domain in the 100-150K temperature regime, tracing the inner parts of the low-mass star-forming region. Therefore, it is necessary to measure and assign its transitions in this range in order to be able to compute accurate predictions required by astronomical observations, in particular with the telescope operating in the submm range, such as ALMA. We present the analysis of mono-deuterated dimethyl ether in its ground-vibrational state, based on an effective Hamiltonian for an asymmetric rotor molecules with internal rotors. The analysis covers the frequency range 150-990GHz. The laboratory rotational spectrum of this species was measured with a submillimeter spectrometer (50-990GHz) using solid-state sources. For the astronomical detection, we used the IRAM 30m telescope to observe a total range of 27GHz, in 4 frequency bands from 100GHz to 219GHz. New sets of spectroscopic parameters have been determined by a least squares fit with the ERHAM code for both conformers. These parameters have permitted the first identification in space of both mono-deuterated DME isomers via detection of twenty transitions in the solar-type protostar IRAS16293-2422 with the IRAM 30m telescope. The DME deuteration ratio in this source appears as high as observed for methanol and formaldehyde, two species known to play an important role in the COMs formation history.