Terahertz spectroscopy and global analysis of the rotational spectrum of
  doubly deuterated Amidogen radical ND$_{2}$
  The deuteration mechanism of molecules in the interstellar medium (ISM) is
still being debated. Observations of deuterium-bearing species in several
astronomical sources represent a powerful tool to improve our understanding of
the interstellar chemistry. The doubly deuterated form of the astrophysically
interesting Amidogen radical could be a target of detection in space. In this
work, the rotational spectrum of the ND$_{2}$ radical in its ground vibrational
and electronic $X^{2}B_{1}$ states has been investigated between 588 and 1131
GHz using a frequency modulation millimeter/submillimeter-wave spectrometer.
The ND$_{2}$ has been produced in a free-space glass absorption cell by
discharging a mixture of ND$_{3}$ and Ar. Sixty-four new transition frequencies
involving $J$ values from 2 to 5 and $K_{a}$ values from 0 to 4 have been
measured. A global analysis including all the previous field-free pure
rotational data has been performed, allowing for a more precise determination
of a very large number of spectroscopic parameters. Accurate predictions of
rotational transition frequencies of ND$_{2}$ are now available from a few GHz
up to several THz.
