2019A&A...622A..82L

Context. The spectra of four low-lying vibrational states of both anti and gauche conformers of normal-propyl cyanide were previously measured and analyzed in two spectral windows between 36 and 127GHz. All states were then identified in a spectral line survey called Exploring Molecular Complexity with ALMA (EMoCA) toward Sagittarius B2(N) between 84.1 and 114.4GHz with the Atacama Large Millimeter/submillimeter Array (ALMA) in its Cycles 0 and 1.
Aims. We wanted to extend the measurements and analysis up to 506GHz to provide accurate predictions over a much wider range of frequencies, quantum numbers and energies.
Methods. We carried out measurements in two additional frequency windows up to 506GHz.
Results. For the gauche conformer, a large number of both a- and b-type transitions were identified. For the anti conformer, transitions were predominantly, but not exclusively, a-type. We hence improved molecular parameters for the ground states of both anti- and gauche-n-propyl cyanide and for excited vibrational states of the gauche conformer (v₃₀=1, v₂₉=1, v₃₀=2, v₂₈=1) and anti conformer (v₃₀=1, v₁₈=1, v₃₀=2, v₂₉=1) with high order coupling parameters determined between v₁₈=1 and v₃₀=2. Parameters are published for the first time for v₁₈=v₃₀=1 of the anti conformer and for v₂₉=v₃₀=1 of the gauche conformer.
Conclusions. In total 15385 lines have been incorporated in the fits and should allow good predictions for unperturbed lines over the whole operating range of radio-telescopes. Evidence is found for vibrational coupling for some levels above 380 GHz. The coupling between v₁₈=1 and v₃₀=2 of the anti conformer has been well characterized. An additional list of 740 lines showing potential but as yet unidentified coupling has been provided for astrophysical identification.