2022ApJ...937...10L

Formamide (NH₂CHO) is considered an important prebiotic molecule because of its potential to form peptide bonds. It was recently detected in the atmosphere of the HH 212 protostellar disk on the solar system scale where planets will form. Here we have mapped it and its potential parent molecules HNCO and H₂CO, along with other molecules CH₃OH and CH₃CHO, in the disk atmosphere, studying its formation mechanism. Interestingly, we find a stratified distribution of these molecules, with the outer emission radius increasing from ∼24 au for NH₂CHO and HNCO, to 36 au for CH₃CHO, to 40 au for CH₃OH, and then to 48 au for H₂CO. More importantly, we find that the increasing order of the outer emission radius of NH₂CHO, CH₃OH, and H₂CO is consistent with the decreasing order of their binding energies, supporting that they are thermally desorbed from the ice mantle on dust grains. We also find that HNCO, which has much lower binding energy than NH₂CHO, has almost the same spatial distribution, kinematics, and temperature as NH₂CHO, and is thus more likely a daughter species of desorbed NH₂CHO. On the other hand, we find that H₂CO has a more extended spatial distribution with different kinematics from NH₂CHO, thus questioning whether it can be the gas-phase parent molecule of NH₂CHO.