From top to bottom: IRAM 30 m, ACA, and ALMA spectra toward the Orion Bar between 345.8 GHz and 345.9 GHz. Blue arrows show the predicted frequencies of the SH⁺, N_J = 1₀−0₁, F = 1/2−1/2 and F = 1/2−3/2 lines before this work (based on experiments by Savage et al. 2004). Red arrows (prediction*) show the expected line frequencies for a Hamiltonian fit that excludes the 345 929.8 MHz line observed by Savage et al. (2004) and attributed to SH⁺; see Sect. 4.