Rotational spectroscopy of n-propanol: Aa and Ag conformers

Context. The primary alcohol n-propanol (i.e., normal-propanol or propan-1-ol; C3H7OH) occurs in five different conformers: Ga, Gg, Gg', Aa, and Ag. All rotational spectra of the three conformers of the G family are well described, making astronomical search of their spectroscopic signatures possible, as opposed to those of the Aa and Ag conformers. Aims. Our goal is to facilitate the astronomical detection of Aa and Ag conformers of n-propanol by characterizing their rotational spectra. Methods. We recorded the rotational spectra of n-propanol in the frequency domain of 18-505 GHz. Additional double-modulation double-resonance (DM-DR) measurements were performed, more specifically with the goal to unambiguously assign weak transitions of the Aa conformer and to verify assignments of the Ag conformer. Results. We derived a spectroscopic quantum mechanical model with experimental accuracy (with J(max) = 70 and K-a,K-max = 6) for Aa n-propanol. Furthermore, we unambiguously assigned transitions (with J(max) = 69 and K-a;max = 9) of Ag n-propanol; in doing so, we prove the existence of two tunneling states, Ag+ and Ag-. Conclusions. The astronomical search of all five conformers of n-propanol is now possible via their rotational signatures. These are applied in a companion article on the detection of n-propanol toward the hot molecular core Sgr B2(N2).