No abstract

The hyperfine structure in the rotational spectrum of water containing (17)O has been investigated experimentally and by means of quantum-chemical calculations. The Lamb-dip technique has been used to resolve the hyperfine structure due to spin-rotation as well as spin-spin interactions and allowed the determination of the corresponding hyperfine parameters with high accuracy. The experimental investigation and, in particular, the analysis of the spectra have been supported by quantum-chemical computations at the coupled-cluster level. The experimental (17)O isotropic spin-rotation constant of H(2)(17)O has been used in a further step for the determination of the paramagnetic part of the corresponding nuclear magnetic shielding constant, whereas the diamagnetic contribution as well as vibrational and temperature corrections have been obtained from quantum-chemical calculations. This joint procedure leads to a value of 325.3(3) ppm for the oxygen shielding in H(2)(17)O at 300 K, in good agreement with pure theoretical predictions, and in this way provides the basis for a new absolute oxygen shielding scale.

Context. Despite the fact that many sulfur-bearing molecules, ranging from simple diatomic species up to astronomical complex molecules, have been detected in the interstellar medium, the sulfur chemistry in space is largely unknown and a depletion in the abundance of S-containing species has been observed in the cold, dense interstellar medium. The chemical form of the missing sulfur has yet to be identified. Aims. For these reasons, in view of the fact that there is a large abundance of triatomic species harbouring sulfur, oxygen, and hydrogen, we decided to investigate the HSO radical in the laboratory to try its astronomical detection. Methods. High-resolution measurements of the rotational spectrum of the HSO radical were carried out within a frequency range well up into the THz region. Subsequently, a rigorous search for HSO in the two most studied high-mass star-forming regions, Orion KL and Sagittarius (Sgr) B2, and in the cold dark cloud Barnard 1 (B1-b) was performed. Results. The frequency coverage and the spectral resolution of our measurements allowed us to improve and extend the existing dataset of spectroscopic parameters, thus enabling accurate frequency predictions up to the THz range. These were used to derive the synthetic spectrum of HSO, by means of the MADEX code, according to the physical parameters of the astronomical source under consideration. For all sources investigated, the lack of HSO lines above the confusion limit of the data is evident. Conclusions. The derived upper limit to the abundance of HSO clearly indicates that this molecule does not achieve significant abundances in either the gas phase or in the ice mantles of dust grains.

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.

No abstract