tokens: also been recently reported in HH 212 in the inner 100 au with a detection of CH 3 CHO and deuterated water HDO (Codella et al. 2016 , 2018 ). Now at higher resolution, we find CH 3 CHO to reside in the disk atmosphere. Moreover, we also detect 8 other organic molecules (H 2 CCO, t-HCOOH, CH 3 OH, CH 2 DOH, 13 CH 3 OH, CH 2 DCN, HCOOCH 3 , and CH 3 CH 2 OH) in the disk atmosphere, with an excitation temperature of ∼150 ± 50 K. Adding 3 other organic molecules (D 2 CO, CH 3 SH and NH 2 CHO) from Lee et al. ( 2017c ), we have 12 organic molecules, with 9 of them being COMs, detected in the disk atmosphere. These results indicate that the hot corino in HH 212 is actually a warm atmosphere of the disk. 4.2. Formation of Organic Molecules We can study the formation of the organic molecules in the disk atmosphere by comparing their abundances to those estimated in the hot corinos around other Class 0 low-mass protostars. The abundance of CH 3 CHO, which is commonly observed in hot corinos, is estimated here to be 3.9 × 10 −9 in HH 212, similar to those found in other hot corinos, e.g., 5.8 × 10 −9 in IRAS 16293-2422B (Jørgensen et al. 2016 ), 2.4 × 10 −9 in B335 (Imai et al. 2016 ), and 4.2 × 10 −9 in NGC 1333 IRAS4A2 (López-Sepulcre et al. 2017 ). To facilitate comparison, we calculate and compare the abundances of the organic molecules relative to CH 3 CHO. Figure 4 shows the comparison of the relative abundances of seven organic molecules (excluding deuterated species and 13 C isotopologue) to those in IRAS 16293-2422B (Jørgensen et al. 2018 ), B335 (Imai et al. 2016 ), and NGC 1333 IRAS4A2 (López-Sepulcre et al. 2017 ). In this comparison, CH 3 SH is excluded because of no reliable measurement of this molecule in other hot corinos to compare with. Interestingly, the relative abundances of most molecules here in HH 212 are similar to those in other hot corinos to within a factor of few, suggesting that the formation of these molecules in the disk atmosphere could be similar to that in other hot corinos. Notice that the abundance of CH 3 SH here is also consistent with that predicted in the hot corino, which can be as high as 5 × 10 −8 (Majumdar et al. 2016 ). Moreover, the abundances here are also similar to those seen in the Class I corino SVS13-A (Bianchi et al. 2019 ) and to those seen in Comet Lovejoy, which shows similar abundances to IRAS 16293-2422B (Biver et al. 2015 ). Figure 4. Comparison of the abundances of organic molecules in the HH 212 disk atmosphere with those in the hot corinos around other low-mass protostars. As shown in Table 2 , our measurements have an uncertainty of about 50%. As discussed in Lee et al. ( 2017c ), the high degree of deuteration in methanol (with [CH 2 DOH]/[CH 3 OH] ∼0.12) and the detection of doubly deuterated formaldehyde suggest that the methanol and formaldehyde in the disk atmosphere are originally formed on icy grains and later desorbed (evaporated) into gas phase due to the heating possibly by
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