High-resolution terahertz spectroscopy of the 15NH radical (widetilde{X 3}Σ-)
Abstract
Context. High-resolution rotational spectroscopy of the imidogen radical has been limited to the 14NH and 14ND isotopologues. Imidogen is an important intermediate in the astronomical synthesis of ammonia. Recently, the 14N/15N isotopic ratio in ammonia has been obtained in cold, dense molecular clouds.
Aims: We conducted a laboratory search for rotational transitions of 15NH to investigate in more detail the 14N/15N ratio in the interstellar medium. Methods.15NH was generated in a positive column discharge in a flowing 15NH3 - He (SOLEIL synchrotron) or 15NH3 - Ar (PhLAM) mixture. High-resolution spectroscopic study of the 15NH isotopologue of imidogen in its ground electronic and vibrational state (widetilde{X ^3}Σ-) was carried out in the THz range (up to 225 cm-1) with the AILES beamline of the SOLEIL synchrotron and subsequently with the PhLAM spectrometer (around 942 GHz). The observed fine and hyperfine structures were analysed, yielding an accurate set of rotational, fine, and hyperfine parameters.
Results: The reported frequencies and molecular constants are suitable for radioastronomical searches of this key species and for 14N/15N isotopic ratio astronomical determination.
- Publication:
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Astronomy and Astrophysics
- Pub Date:
- February 2012
- DOI:
- 10.1051/0004-6361/201118129
- Bibcode:
- 2012A&A...538A.135B
- Keywords:
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- line: identification;
- molecular data;
- ISM: molecules;
- submillimeter: ISM