We have searched for interstellar conformer I glycine (NH 2CH2COOH), the simplest amino acid, in the hot molecular cores Sgr B2(N-LMH), Orion KL, and W51 el/e2. An improved search strategy for intrinsically weak molecular lines, involving multisource observations, has been developed and implemented. In total, 82 spectral frequency bands, in the millimeter-wave region, were observed over a 4 yr period; 27 glycine lines were detected in 19 different spectral bands in one or more sources. The rotational temperatures derived from "rotation diagrams" are 75 -16+29 K for Sgr B2(N-LMH), 141-37 +76 K for Orion KL, and 121-32+71 K for W51 el/e2. The total column densities inferred are 4.16-1.82 +3.22 × 1014 cm-2 for Sgr B2, 4.37 -1.27+1.79 × 1014 cm-2 for Orion, and 2.09-0.77+1.22 × 1014 cm -2 for W51. Production of interstellar glycine by both gas-phase ion-molecule reactions and by ultraviolet photolysis of molecular ices is briefly discussed. The discovery of interstellar glycine strengthens the thesis that interstellar organic molecules could have played a pivotal role in the prebiotic chemistry of the early Earth.
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