SIMBAD references

Observations of IRC +10216 with the Yebes 40 m telescope between 31 and 50 GHz have revealed more than 150 unidentified lines. Some of them can be grouped into a new series of 26 doublets, harmonically related with integer quantum numbers ranging from J_up=54 to 80. The separation of the doublets increases systematically with J, that is to say, as expected for a linear species in one of its bending modes. The rotational parameters resulting from the fit to these data are B=290.8844±0.0004MHz, D=0.88±0.04Hz, and q=0.1463±0.0001MHz. The rotational constant is very close to that of the ground state of HC₉N. Our ab initio calculations show an excellent agreement between these parameters and those predicted for the lowest energy vibrationally excited state, ν₁₉=1, of HC₉N. This is the first detection, and complete characterization in space, of vibrationally excited HC₉N. An energy of 41.5cm^–1 is estimated for the ν₁₉ state. In addition, 17 doublets of HC₇N in the ν₁₅=1 state, for which laboratory spectroscopy is available, were detected for the first time in IRC +10216. Several doublets of HC₅N in its ν₁₁=1 state were also observed. The column density ratio between the ground and the lowest excited vibrational states are ≃127, 9.5, and 1.5 for HC₅N, HC₇N, and HC₉N, respectively. We find that these lowest-lying vibrational states are most probably populated via infrared pumping to vibrationally excited states lying at ≃600cm^–1. The lowest vibrationally excited states thus need to be taken into account to precisely determine absolute abundances and abundance ratios for long carbon chains. The abundance ratios N(HC₅N)/N(HC₇N) and N(HC₇N)/N(HC₉N) are 2.4 and 7.7, respectively.