Laboratory rotational spectroscopy of acrylamide and search for
  acrylamide and propionamide toward Sgr B2(N) with ALMA
  Numerous complex organic molecules have been detected in the universe among
which amides are considered as models for species containing the peptide
linkage. Acrylamide bears in its backbone not only the peptide bond, but also
the vinyl functional group which is a common motif in many interstellar
compounds. This makes acrylamide an interesting target for a search in space.
In addition, a tentative detection of the related molecule propionamide has
been recently claimed toward Sgr B2(N). We report accurate laboratory
measurements and analyses of thousands rotational transitions for the syn and
skew forms of acrylamide between 75 and 480 GHz. Tunneling through a low energy
barrier between two symmetrically equivalent configurations has been revealed
for the higher-energy skew species. We searched for emission of acrylamide in
the imaging spectral line survey ReMoCA performed with ALMA toward Sgr B2(N).
We also searched for propionamide in the same source. Neither acrylamide nor
propionamide were detected toward the two main hot molecular cores of Sgr
B2(N). We did not detect propionamide either toward a position located to the
east of the main hot core, thereby not confirming the recent claim of its
interstellar detection toward this position. We find that acrylamide and
propionamide are at least 26 and 14 times, respectively, less abundant than
acetamide toward the main hot core Sgr B2(N1S), and at least 6 and 3 times,
respectively, less abundant than acetamide toward the secondary hot core Sgr
B2(N2). A comparison with results of astrochemical kinetics model for related
species suggests that acrylamide may be a few hundred times less abundant than
acetamide, corresponding to a value at least an order of magnitude lower than
the observational upper limits. Propionamide may be as little as only a factor
of two less abundant than the upper limit derived toward Sgr B2(N1S).
