Observed spectra (black) and the XCLASS modeled spectra (red) in a scale, toward W3 IRS5, W3(OH), and NGC 753 8 IRS1 from left to right. The spectra in each panel correspond to HCO⁺, HCN, HNC, CS, H₂S, C₂H, and c-C₃H₂, from top to bottom. The shaded areas indicate velocity intervals of the local arm in cyan and the Perseus arm in gray. The υ_sys of the continuum sources are indicated using vertical dashed lines.