Frequency measurement of pure rotational transitions of molecular ions important in interstellar chemistry

Frequencies of pure rotational transitions of molecular anions or cations which are interested in the studies of interstellar chemistry are measured precisely by using a tunable terahertz spectrometer in Toyama. In the investigation of OD^-, isotope independent Dunham parameters were obtained. As for the H₂D⁺ cation, the frequency of the 2₁₂larr1₁₁ transition which was detected recently in space was measured precisely and a new set of rotational parameters were obtained.