The Prebiotic Molecular Inventory of Serpens SMM1: II. The Building Blocks of Peptide Chains

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Abstract

This work aims to constrain the abundances of interstellar amides, by searching for this group of prebiotic molecules in the intermediate-mass protostar Serpens SMM1-a. ALMA observations are conducted toward Serpens SMM1. A spectrum is extracted toward the SMM1-a position and analyzed with the CASSIS line analysis software for the presence of characteristic rotational lines of a number of amides and other molecules. NH
₂CHO, NH
₂CHO ν
₁₂= 1, NH
₂
¹³CHO, CH
₃C(O)NH
₂ν = 0, 1, CH
₂DOH, CH
₃CHO, and CH
₃C(O)CH
₃are securely detected, while trans-NHDCHO, NH
₂CDO, CH
₃NHCHO ν = 0, 1, CH
₃COOH, and HOCH
₂CHO are tentatively identified. The results of this work are compared with detections presented in the literature. A uniform CH
₃C(O)NH
₂/NH
₂CHO ratio is found for a group of interstellar sources with vast physical differences. A similar ratio is seen for CH
₃NHCHO, based on a smaller data sample. The D/H ratio of NH
₂CHO is about 1-3% and is close to values found in the low-mass source IRAS 16293-2422B. The formation of CH
₃C(O)NH
₂and NH
₂CHO is likely linked. Formation of these molecules on grain surfaces during the dark cloud stage is a likely scenario. The high D/H ratio of NH
₂CHO is also seen as an indication that these molecules are formed on icy dust grains. As a direct consequence, amides are expected to be present in the most pristine material from which planetary systems form, thus providing a reservoir of prebiotic material.