Left: rotational energy levels of NH₃ (see the LAMDA data bank, Schöier et al. 2005). Energies up to 800 K are given for the ortho-NH₃ states (K = 0 or K = multiple of 3), whereas these are roughly half for para-NH₃ (K ≠ 0 and K ≠ multiple of 3). All levels are plotted to scale, rendering the inversion splittings unresolved. Middle: same as left frame, but for energies below 100 K. For symmetry reasons, half of the inversion levels do not exist for K = 0. In this panel, the inversion levels, shown to scale, are resolved. Right: hyperfine splitting, due to quadrupole interaction, of the (J = 1,K = 0) level is shown. The resulting shifts, in km s^-1, for the NH₃ (1₀−0₀) line are indicated next to the components. The drawing is to scale and energies are in milli-Kelvin.