Frequency measurement of pure rotational transitions of OD−

Frequencies of pure rotational transitions of OD− have been measured in the 1-5 THz region using a high-precision tunable far-infrared spectrometer based on difference frequency of two CO2 lasers. The measured frequencies were analyzed together with the data in the infrared and the sub-millimeter region to refine the rotational parameters. Isotopically invariant Dunham parameters were also obtained.