(a) Averaged spectra of ¹³CO (J = 2–1) (black) and C¹⁸O (J = 2–1) (red) over the hub–filament cloud of G326. The intensity of C¹⁸O (J = 2–1) has been reduced by a scale factor of 5 for ease of viewing. The vertical dashed lines show the velocity interval −41.5 to −33.0 km s⁻¹ over which the infrared dark hub–filament cloud of G326 extends. (b) Beam-averaged spectra of ¹³CO (J = 2–1) (black) and C¹⁸O (J = 2–1) (red) for C1. (c) Same as panel (b), but for C2. (d) Same as panel (b), but for C3.