Loomis-Wood plot of Aa n-propanol - screenshot of the LLWP software (Bonah et al. 2022). Shown here is a doublet series (A and E components of the methyl group internal rotation) of the J_3,J-3 ← J_2,J-2 b-type transitions from J = 6 (bottom panel) to J = 36 (top panel). Predictions of the A components are set as center frequencies and are depicted by green sticks. The E components are depicted by red ones. This ^rQ series with K_a + K_c = J and ΔΚ_a, ΔK_c = +1,-1 is well reproduced by our spectroscopic model described in Table 2 up to J = 22, however, transitions up to J = 41 (Δ_ν ≈ 90 MHz) are straightforwardly assignable.