The Rotation‐Inversion Spectrum of Isocyanamide, H2N — NC, in the Millimeter Wave Region

The rotation‐inversion spectrum of isocyanamide, H2N — NC, has been investigated in the frequency range 100 to 400 GHz. Due to the near C2v symmetry of the inverting molecule two types of dipole transitions have been observed: 1) intrasystem a‐type transitions and 2) intersystem or rotation‐inversion c‐type transitions connecting the two energy manifolds of H2N — NC belonging to the inversion states O+ and O−, respectively. The inversion splitting was found to be 0.369 cm−1, indicative of a high barrier to inversion. Pure inversion transitions are not allowed. The rotation‐inversion analysis was carried out for 240 a‐type and c‐type transitions using S‐reduced Hamiltonians according to Watson for the O+ and O− inversion states separated by the inversion splitting E1nv. The analysis yielded the following spectroscopic constants: magnified image plus centrifugal distortion constants. The present data and their analysis provide an excellent basis for a radioastronomical search for H2N — NC.