The prebiotic molecular inventory of Serpens SMM1: II. The building
  blocks of peptide chains
  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$_{2}$CHO, NH$_{2}$CHO $\nu_{12}$=1,
NH$_{2}^{13}$CHO, CH$_{3}$C(O)NH$_{2}$ $\nu$=0,1, CH$_{2}$DOH, CH$_{3}$CHO, and
CH$_{3}$C(O)CH$_{3}$ are securely detected, while trans-NHDCHO, NH$_{2}$CDO,
CH$_{3}$NHCHO $\nu$=0,1, CH$_{3}$COOH, and HOCH$_{2}$CHO are tentatively
identified. The results of this work are compared with detections presented in
the literature. A uniform CH$_{3}$C(O)NH$_{2}$/NH$_{2}$CHO ratio is found for a
group of interstellar sources with vast physical differences. A similar ratio
is seen for CH$_{3}$NHCHO, based on a smaller data sample. The D/H ratio of
NH$_{2}$CHO is about 1--3\% and is close to values found in the low-mass source
IRAS~16293--2422B. The formation of CH$_{3}$C(O)NH$_{2}$ and NH$_{2}$CHO 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$_{2}$CHO 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.
