Average spectra of DCO⁺, DNC, and DCN, and their ¹³C-isotopologs in the DR21 filament. The black line shows the spectra averaged over the entire mapped region of the DR21 filament for different molecules with the purple region showing the velocity range used for determining integrated intensities. The dashed gray line denotes the main velocity of the filament, υ_LSR = −3 km s⁻¹. The velocities of the un- or only marginally blended HFS components of DCN and H¹³CN are marked in black, with the relative intensity of the hyperfine components marked by the length. The LSR velocity scale of the DCN and H¹³CN J = 1−0 spectra corresponds to the strongest HFS component F = 2−1.