Clockwise from the top left: MOLPOP-CEP non-LTE radiative-transfer modelling of the CH ground-state transitions towards Sgr B2 (M) for LOS velocity components at −58, and +8 km s⁻¹ followed by those associated with the envelope at υ_LSR = +76, +67, and +57 km s⁻¹, respectively. Displayed in red and blue curves (central plot) are the modelled line ratios which best reproduce the observed line ratios between the 3.264 GHz, and 3.349 GHz lines and those between the 3.335 GHz and 3.349 GHz lines and their uncertainties, respectively, as a function of n and T_kin. The corner plots display the gas density and temperature distributions as governed by the 3 σ level of the minimum χ² with the median and standard deviation marked by the solid and dashed teal lines, respectively.