Direct absorption observation of the van der Waals bending band of ArHCN by millimeterwave spectroscopy combined with pulsed-jet expansion technique

Millimeterwave absorption spectroscopy combined with the pulsed-jet expansion technique was applied to the measurement of rovibrational transitions in the van der Waals band of ArHCN near 200 GHz. Observations were extended to the higher millimeterwave frequency region up to 260 GHz, and 17 rovibrational transitions split into hyperfine components due to the nitrogen nucleus were newly observed for both the Σ1–Σ0 and Π1–Σ0 bands. An improved set of molecular constants, including the band origins, rotational constants, quadrupole coupling constants, and the Coriolis coupling constant between the Σ1 and Π1 bending substrates, was determined.