Reduced energy diagram of Ag n-propanol. The reduced energy is E_red = Ε_T + E_rot - J • (J + 1) • (B + C)/2. Thereby, the energies of the rotational levels E_rot are calculated based on ab initio calculations of Kisiel et al. (2010). We used the same parameters for both tunneling states as ab initio calculations are presented for a single state only. We note that actual parameters of the two tunneling states will differ. We set the energy difference of the two tunneling states to 3 cm⁻¹, i.e. and , on the assumption that the splitting is similar to what has been observed for gauche-ethmol (Pearson et al. 1997). (a) The reduced energy diagram for rotational energy levels with K_a < 9 shows that series with K_a > 5 may not cross each other. We note that it may happen if different rotational parameters for the two tunneling states are taken into account, (b) The reduced energy diagram for rotational energy levels with K_a < 4 is a zoom of the y-axis of (a). We note that many series cross each other and even though the exact energy difference between the two tunneling states Ag⁺ and Ag^- is unknown so far, many tunneling-rotation interactions occur in this region and determining an accurate energy difference is essential to properly take them into account.