Observed H₂CO (1_1,0–1_1,1) spectrum at an HPBW of 10′.8 toward DR21 (solid black line) overlaid with the fitted model (solid blue line). The two velocity components at −3 km s⁻¹ and 8 km s⁻¹ correspond to two physically distinct velocity components that arise from the DR21 cloud and its foreground cloud associated with W75N. The fitted HFS components are indicated by the colored dashed lines in the legend.