Spectra of [O I] and HF absorption toward Sgr B2(M) divided by the corresponding continua. Upper: SOFIA/GREAT [O I] spectrum. The lower histogram shows the difference between two independent data subsets divided by 2, which is a measure of the uncertainty in the [O I] spectrum. Gray areas show velocities excluded from the analysis. This includes the Sgr B2 envelope at velocities greater than 40 km s⁻¹ and the region between −6 and 0 km s⁻¹, where the [O I] spectrum is contaminated by telluric absorption. Lower: Average Herschel/HIFI spectrum of HF. The lower histogram shows the difference between the two independent observations divided by 2, which is a measure of the uncertainty in the average spectrum.