Fortrat diagram of n-propanol. Top panel: a broadband measurement in the W-band region is shown, where respective regions with signatures of the Ag conformer, leading to the Fortrat diagram, are highlighted. In some regions, the spectrometer is not as sensitive, e.g. around J=11, compared to others. Bottom panel: The colored lines in the Fortrat diagram mark linkages of series transitions, . DM-DR spectroscopy secured assignments in the W-band region (from J = 10 to J = 16). The existence of two tunneling states is proven as for each K_a partner series are found; the tunneling states are marked by 0⁺ and 0⁻. More series can be found, but are not assigned yet, e.g. ^QR₃ ones. We note the larger tunneling splitting of ^QR₆ series (green lines), e.g., in comparison to ^QR₅ ones, and the different slopes for ^QR_S series (thick purple lines).