From top to bottom: N, J = 2, 3∕2 → 1, 1∕2 transition spectra of ¹³CH and CH near 1997 and 2006 GHz, in black with their corresponding Wiener filter fits to the spectra overlaid in red towards Sgr B2(M) (left) and G34.26+0.15 (right). Followed by their Wiener filter deconvolved spectra displayed in grey in optical depth scales. The ¹²CH spectrum towards Sgr B2(M) is contaminated by C₃ absorption at 2004.833 GHz in the image band, as indicated in blue.