Discovery of the ubiquitous cation NS+ in space confirmed by laboratory
  spectroscopy
  We report the detection in space of a new molecular species which has been
characterized spectroscopically and fully identified from astrophysical data.
The observations were carried out with the 30m IRAM telescope. The molecule is
ubiquitous as its $J$=2$\rightarrow$1 transition has been found in cold
molecular clouds, prestellar cores, and shocks. However, it is not found in the
hot cores of Orion-KL and in the carbon-rich evolved star IRC+10216. Three
rotational transitions in perfect harmonic relation J'=2/3/5 have been
identified in the prestellar core B1b. The molecule has a 1Sigma electronic
ground state and its J=2-1 transition presents the hyperfine structure
characteristic of a molecule containing a nucleus with spin 1. A careful
analysis of possible carriers shows that the best candidate is NS+. The derived
rotational constant agrees within 0.3-0.7 % with ab initio calculations. NS+
was also produced in the laboratory to unambiguously validate the astrophysical
assignment. The observed rotational frequencies and determined molecular
constants confirm the discovery of the nitrogen sulfide cation in space. The
chemistry of NS+ and related nitrogen-bearing species has been analyzed by
means of a time-dependent gas phase model. The model reproduces well the
observed NS/NS+ abundance ratio, in the range 30-50, and indicates that NS+ is
formed by reactions of the neutral atoms N and S with the cations SH+ and NH+,
respectively.
