The rotational spectra of the ground and first excited bending states of deuterium isocyanide, DNC, up to 2Â THz

The pure rotational spectrum of deuterium isocyanide (DNC) was recorded in the frequency range from approximately 680 to 1985 GHz. Twenty-one new transitions in the vibrational ground and first excited bending states (01e,f 0) have been assigned, namely R-branch transitions from J=9←8 to 25←24. In a least squares analysis of these new transition frequencies together with previously reported millimeter-wave data, spectroscopic parameters up to sextic order could be derived with high precision for both states. Furthermore, the ℓ-type doubling constant q and its centrifugal distortion terms qJ and qJJ were obtained for the first excited bending state.