SIMBAD references

We report new laboratory spectroscopic data on the rotational spectrum of the pyrimidine nucleic acid base uracil (C₄H₄N₂O₂). The dataset has been extended both into the microwave region and towards mm-wavelengths with the aim of providing accurate transition rest frequencies for astrophysical searches. The microwave measurements have been performed with a molecular beam Fourier transform microwave spectrometer in the frequency range from 9-19GHz and the mm-wave band transitions have been recorded with a Stark-modulated free jet spectrometer up to 100GHz. The global dataset has been analysed with a standard S-reduced Hamiltonian and precise spectroscopic parameters up to quartic order have been obtained. The hyperfine structure due to the two ¹⁴N nuclei has been resolved in the microwave measurements and the nuclear quadrupole coupling constants could be derived to high accuracy. Based on the new laboratory data and analysis, highly precise rotational transition rest frequencies are available for astrophysical important lines of uracil up to 300GHz.