Terahertz Spectroscopy and Global Analysis of the Rotational Spectrum of Doubly Deuterated Amidogen Radical ND2

The deuteration mechanism of molecules in the interstellar medium 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 ND₂ radical in its ground vibrational and electronic {X}²{B}₁ state has been investigated between 588 and 1131 GHz using a frequency modulation millimeter/submillimeter-wave spectrometer. The ND₂ molecule has been produced in a free-space glass absorption cell by discharging a mixture of ND₃ 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 ND₂ are now available from a few gigahertz up to several terahertz.