Spectra of B0415+379 and B0355+508 at the frequencies of H₂CO 1_0,1–0_0,0 (72 837.949 MHz) and of the strongest hyperfine component of H₂NC and H₂CN (72194.211 MHz and 73 349.648 MHz, respectively). The y-axis is expressed as line/continuum. The position of the deepest absorption of H₂CO, V_LSR = −0.9 km s⁻¹ in B0415+379 and V_LSR = −10.4 km s⁻¹ in B0355+508, is indicated by a vertical dotted blue line.