  For all the amides detected in the interstellar medium (ISM), the
corresponding nitriles or isonitriles have also been detected in the ISM, some
of which have relatively high abundances. Among the abundant nitriles for which
the corresponding amide has not yet been detected is cyanoacetylene (HCCCN),
whose amide counterpart is propiolamide (HCCC(O)NH$_2$). With the aim of
supporting searches for this amide in the ISM, we provide a complete rotational
study of propiolamide from 6 GHz to 440 GHz using rotational spectroscopic
techniques in the frequency and time domain. We identified and measured more
than 5500 distinct frequency lines of propiolamide and obtained accurate sets
of spectroscopic parameters for the ground state and the three low-lying
excited vibrational states. We used the ReMoCA spectral line survey performed
with the Atacama Large Millimeter/submillimeter Array toward the star-forming
region Sgr B2(N) to search for propiolamide. We report the nondetection of
propiolamide toward the hot cores Sgr B2(N1S) and Sgr B2(N2). We find that
propiolamide is at least 50 and 13 times less abundant than acetamide in Sgr
B2(N1S) and Sgr B2(N2), respectively, indicating that the abundance difference
between both amides is more pronounced by at least a factor of 8 and 2,
respectively, than for their corresponding nitriles. Although propiolamide has
yet to be included in astrochemical modeling networks, the observed upper limit
to the ratio of propiolamide to acetamide seems consistent with the ratios of
related species as determined from past simulations.
