Abstract. We present the first laboratory measurements of the hyperfine structure of the J = 1 ← 0 rotational transition of N 2 D + , a good tracer of the dense regions of molecular cloud cores, and the spectra of unresolved high J transitions recorded in the 308−463 GHz region. Together with a high sensitivity radio-astronomical spectrum of the N 2 D + J = 1 → 0 rotational transition in a quiescent cloud core, we determined with high precision the frequencies of the seven hyperfine components and the molecular spectroscopic constants, allowing us to make predictions on the N 2 D + frequencies of higher J transitions occurring in the submillimeter-wave region.
Rotational transitions of DCO+ in vibrationally excited states were measured in the region 360–440 GHz. The states investigated are: 0 2 0 (with l=0,2), 0 3 0 (with l=1,3), 0 4 0 (with l=0,2,4), 0 11 1, and 1 00 0. This study allowed us to carefully analyze the vibrational interaction affecting the first C–D stretching state 1 00 0, which was confirmed to be due to the 0 11 1 state. Taking account of the perturbation effect on the rotational constants of the involved states allowed to derive an accurate equilibrium structure of HCO+, which resulted to be rCH=1.092 04 Å and rCO=1.105 58 Å.
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