SIMBAD references

The rotational spectra of ²⁹SiC₂ and ³⁰SiC₂, two silicon isotopic species of the abundant astronomical ring ²⁸SiC₂, have been characterized in the millimeter band between 140 and 360 GHz in a low pressure discharge through SiH₄, C₂H₂, and Ar. Precise rotational and centrifugal distortion constants have been derived for both species by fitting a standard asymmetric top Hamiltonian to 38 a-type transitions of ²⁹SiC₂ and 35 of ³⁰SiC₂; the data sets include transitions up to K_a= 8 and at least J = 16. With these new measurements in hand, the most intense radio transitions of both species either have been measured or can now be predicted to better than 1 km/s in equivalent radial velocity up to 500 GHz, more than adequate accuracy for spectral line identifications in circumstellar shells of evolved carbon stars such as IRC+10216 where SiC₂ is conspicuous. More than 10 new lines of ²⁹SiC₂ and ³⁰SiC₂have been identified between 295 and 354 GHz in the interferometric spectral line survey of IRC+10216 with the Submillimeter Array.