Context. Numerous complex organic molecules have been detected in the universe and among them are amides, which are considered as prime models for species containing a peptide linkage. In its backbone, acrylamide (CH 2 CHC(O)NH 2 ) bears not only the peptide bond, but also the vinyl functional group that is a common structural feature in many interstellar compounds. This makes acrylamide an interesting candidate for searches in the interstellar medium. In addition, a tentative detection of the related molecule propionamide (C 2 H 5 C(O)NH 2 ) has been recently claimed toward Sgr B2(N). Aims. The aim of this work is to extend the knowledge of the laboratory rotational spectrum of acrylamide to higher frequencies, which would make it possible to conduct a rigorous search for interstellar signatures of this amide using millimeter wave astronomy. Methods. We measured and analyzed the rotational spectrum of acrylamide between 75 and 480 GHz. We searched for emission of acrylamide in the imaging spectral line survey ReMoCA performed with the Atacama Large Millimeter/submillimeter Array toward Sgr B2(N). We also searched for propionamide in the same source. The astronomical spectra were analyzed under the assumption of local thermodynamic equilibrium. Results. We report accurate laboratory measurements and analyses of thousands of rotational transitions in the ground state and two excited vibrational states of the most stable syn form of acrylamide. In addition, we report an extensive set of rotational transitions for the less stable skew conformer. Tunneling through a low energy barrier between two symmetrically equivalent configurations has been revealed for this higher-energy species. 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 undermining the recent claim of its interstellar detection toward this position. We find that acrylamide and propionamide are at least 26 and 14 times less abundant, respectively, than acetamide toward the main hot core Sgr B2(N1S), and at least 6 and 3 times less abundant, respectively, than acetamide toward the secondary hot core Sgr B2(N2). Conclusions. 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 that is 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). Lastly, the spectroscopic data presented in this work will aid future searches of acrylamide in space.

Context. The interstellar detections of isocyanic acid (HNCO), methyl isocyanate (CH 3 NCO), and very recently also ethyl isocyanate (C 2 H 5 NCO), open the question of the possible detection of vinyl isocyanate (C 2 H 3 NCO) in the interstellar medium. There are only low-frequency spectroscopic data (< 40 GHz) available for this species in the literature. This makes predictions at higher frequencies rather uncertain hampering its search in space by millimeter wave astronomy. Aims. The aim of the present study is, on one hand, to extend the laboratory rotational spectrum of vinyl isocyanate into the millimeter wave region and, on the other hand, to undertake a first check for its presence in the high-mass star forming region Sgr B2, where other isocyanates and a plethora of complex organic molecules are observed. Methods. The pure rotational spectrum of vinyl isocyanate was recorded in the frequency regions 127.5-218 and 285-330 GHz using the Prague millimeter wave spectrometer. The spectral analysis was supported by high-level quantum-chemical calculations. On the astronomy side, we assumed local thermodynamic equilibrium to compute synthetic spectra of vinyl isocyanate and to search for it in the ReMoCA survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA) toward the high-mass star forming protocluster Sgr B2(N). Additionally, we searched for the related molecule ethyl isocyanate in the same source.Results. Accurate values for the rotational and centrifugal distortion constants are reported for the ground vibrational states of trans and cis vinyl isocyanate from the analysis of more than 1000 transitions. We report nondetections of vinyl and ethyl isocyanate toward the main hot core of Sgr B2(N). We find that vinyl and ethyl isocyanate are at least 11 and 3 times less abundant than methyl isocyanate in this source, respectively. Conclusions. Although the precise formation mechanism of interstellar methyl isocyanate itself remains uncertain, we infer from existing astrochemical models that our observational upper limit for the CH 3 NCO:C 2 H 5 NCO ratio in Sgr B2(N) is consistent with ethyl isocyanate being formed on dust grains via the abstraction or photodissociation of an H atom from methyl isocyanate, followed by the addition of a methyl radical. The dominance of such a process for ethyl isocyanate production, combined with the absence of an analogous mechanism for vinyl isocyanate, would indicate that the ratio C 2 H 3 NCO:C 2 H 5 NCO should be rather less than unity. Even though vinyl isocyanate was not detected toward Sgr B2(N), results of this work represent a significant improvement on previous low-frequency studies and will allow the astronomical community to continue in searching for this species in the universe.

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The saturated part of the 1,2,3,4-tetrahydroquinoline (THQ) molecule allows for the possibility of multiple conformers' existence. High-resolution microwave spectroscopy, supported by high-level quantum chemistry calculations, was used to determine the precise molecular structures of the conformers of THQ. Via the MP2 calculations, we were able to discriminate four stable conformations, i.e. two pairs of energetically equivalent enantiomorphic conformers. The results of the calculations also indicate that energetically non-equivalent conformers are separated by a low energy barrier (104 cm-1) that allows for conformational cooling to occur. The high resolution rotational spectrum with resolved hyperfine structure in the frequency range of 7-20 GHz was obtained using both the In-phase/quadrature-phase-Modulation Passage-Acquired-Coherence Technique (IMPACT) and the coaxially oriented beam resonator arrangement (COBRA) to perform Fourier transform microwave (FTMW) spectroscopy. The precise values of the rotational constants, 14N nuclear hyperfine coupling parameters and centrifugal distortion parameters were determined from the measured transition frequencies. Based on our experimental results, only the most stable enantiomeric pair of THQ contributes to the rotational spectrum under the conditions of our experiment as the less stable conformers seem to efficiently relax to the lower energy conformers. Thus the experimentally evaluated molecular constants unambiguously define the lowest energy conformer of 1,2,3,4-tetrahydroquinoline.