Rotational spectroscopic study and astronomical search for propiolamide in Sgr B2(N)

TL;DR

This study provides a comprehensive rotational spectroscopic analysis of propiolamide and searches for it in the interstellar medium, specifically in Sgr B2(N), but finds it to be less abundant than related amides, informing astrochemical models.

Contribution

The paper offers the first complete rotational spectroscopic data for propiolamide and applies this to astronomical observations, setting upper limits on its abundance in Sgr B2(N).

Findings

Propiolamide was not detected in Sgr B2(N) hot cores.

Propiolamide is at least 50 and 13 times less abundant than acetamide.

The abundance ratio of propiolamide to acetamide is lower than that of their nitrile counterparts.

Abstract

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.