Overview of the N′ − N″ = 18–17 a-type transition of H₂NCO observed experimentally and comparison with a 300 K simulation obtained using the final spectroscopic constants (Table 1). The lowest K_a values are reported for both asymmetric components in the upper panel (in blue and purple). The lower panel corresponds to a zoom into the K_a = 3–12 region highlighted in light purple in the upper panel. The area highlighted in orange displays a partially resolved hyperfine structure (K_a = 3). The simulation was obtained using a Gaussian profile with a full width at half maximum of 1.3 MHz; the second derivative of the PGOPHER trace is plotted for visual comparison with the experimental spectrum.