Ratio of HBr to HCℓ abundance in the NGC 6334I Hot Core and the Orion KL Plateau (upper limits for both sources) and pure gas-phase chemical models (1, 2, 3; see text), and in comet 67P/C–G (Dhooghe et al. 2017). We also show the elemental Cℓ/H₂ and Br/Cℓ ratios for meteorites (red circle) and the sun (orange line; the solar Br abundance is unknown). Models are shown for n_H = 10⁶ cm⁻³ and T_kin = 150 K. Variations of ± 1 in log (n_H) and ± 50 K in T_kin induce negligible and 0.5 dex variations, respectively. Model 1 has all elemental Cℓ and Br in the gas; in 2 only Cℓ, and in 3 both Cℓ and Br are depleted from the gas by a factor of 100.