The extremely young Class 0 object B1b-S and the first hydrostatic core (FSHC) candidate, B1b-N, provide a unique opportunity to study the chemical changes produced in the elusive transition from the prestellar core to the protostellar phase. We present 40x70 images of Barnard 1b in the 13CO 1->0, C18O 1->0, NH2D 1_{1,1}a->1_{0,1}s, and SO 3_2->2_1 lines obtained with the NOEMA interferometer. The observed chemical segregation allows us to unveil the physical structure of this young protostellar system down to scales of ~500au. The two protostellar objects are embedded in an elongated condensation, with a velocity gradient of ~0.2-0.4 m s^{-1} au^{-1} in the east-west direction, reminiscent of an axial collapse. The NH2D data reveal cold and dense pseudo-disks (R~500-1000 au) around each protostar. Moreover, we observe evidence of pseudo-disk rotation around B1b-S. We do not see any signature of the bipolar outflows associated with B1b-N and B1b-S, which were previously detected in H2CO and CH3OH, in any of the imaged species. The non-detection of SO constrains the SO/CH3OH abundance ratio in the high-velocity gas.
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