Torsional-rotational spectrum of doubly-deuterated dimethyl ether
  (CH$_3$OCHD$_2$) -- First ALMA detection in the interstellar medium
  In 2013, we have published the first rotational analysis and detection of
mono-deuterated dimethyl ether in the solar-type protostar IRAS 16293-2422 with
the IRAM 30m telescope. Dimethyl ether is one of the most abundant complex
organic molecules (COMs) in star-forming regions and their D-to-H (D/H) ratios
is important to understand its chemistry and trace the source history. We
present the first analysis of doubly-deuterated dimethyl ether
(methoxy-d2-methane, 1,1-dideuteromethylether) in its ground-vibrational state,
based on an effective Hamiltonian for an asymmetric rotor molecules with
internal rotors. The analysis covers the frequency range 0.15-1.5THz. The
laboratory rotational spectrum of this species was measured between 150 and
1500 GHz with the Lille's submillimeter spectrometer. For the astronomical
detection, we used the Atacama Large Millimeter/submillimeter Array (ALMA)
observations from the Protostellar Interferometric Line Survey, PILS. New sets
of spectroscopic parameters have been determined by a least squares fit with
the ERHAM code for both symmetric and asymmetric conformers. As for the
mono-deuterated species, these parameters have permitted the first
identification in space of both conformers of a doubly-deuterated dimethyl
ether via detection near the B component of the Class 0 protostar IRAS
16293-2422.
