Left: observed Hα, Heα, and Cα transitions for n = 75 toward W3 IRS5. The LSR velocity scale is given with respect to the Cα line at 15.82 GHz. The pink dashed curve represents the fit to the He RRL and the shaded purple region confines the CRRL. Right: decomposed CRRL profile in blue alongside the 68 and 70 GHz HFS-stacked CH₂ line profiles displayed by the dashed orange and dashed-dotted violet curves, respectively. The stacked profile of the 70 GHz CH₂ transition was obtained from the HFS decomposition model. The hatched grey regions display the line profile of the ³ P₁ − ³ P₀ transition of CI at 492.160 GHz scaled down by a factor of 125 on the T_mb scale.