Bold dark line: spectrum of Mars between 1233.9 and 1234.1 cm⁻¹, integrated over the southern hemisphere of the planet, recorded on May 7, 2016 (Ls = 148Å, normalized radiance). Thin lines: synthetic models, calculated using the atmospheric parameters described in Sect. 2.2: Black: H₂O₂ = 0 ppbv; green: H₂O₂ = 20 ppbv; red: H₂O₂ = 40 ppbv; blue: H₂O₂ = 60 ppbv. H₂O₂ is undetected, with a 2σ upper limit of 10 ppbv. The poor fit of the CO₂ line in the southern hemisphere is due to the occasional presence of a spike near the line center. The spectral resolution of the models is 0.024 cm⁻¹.