Interstellar glycolamide: A comprehensive rotational study and an astronomical search in Sgr B2(N)

Characterization of the Coriolis Coupled Far-Infrared Bands of syn-Vinyl Alcohol

Rotational emission from vibrationally excited molecules are responsible for a large fraction of lines in the spectra of interstellar molecular clouds. Vinyl alcohol (VA) has two rotamers that differ in energy by 6.4 kJ/mol, both of which have been observed toward the molecular cloud, Sagittarius B2(N) [Turner and Apponi, Astrophys. J. 2001, 561, 207]. Previously, we reported an analysis of the far-infrared spectrum of the higher energy rotamer, anti-VA [Bunn et al. Astrophys. J. 2017, 847, 67], yielding rotational and higher order distortion constants in the first excited vibrational state, and here, we report an analysis of the far-infrared spectrum of the lower energy rotamer, syn-VA, whose spectrum is significantly more complicated on account of Coriolis interactions that result in perturbations to the rovibrational spectrum. We account for those perturbations with the inclusion of Coriolis coupling constants in the fit, which couples the first excited OH torsional (ν₁₅) and CCO bending (ν₁₁) states. Inclusion of them resulted in more physically meaningful rotational and centrifugal distortion constants, and allows for accurate pure rotational line predictions to be made up to high energies. These will be particularly useful in searches for vibrationally excited syn-VA toward warm regions of interstellar molecular clouds, where we predict that it may be significantly abundant.

Laboratory Detection of Cyanoacetic Acid: A Jet-Cooled Rotational Study

Herein we present a laboratory rotational study of cyanoacetic acid (CH2(CN)C(O)OH), an organic acid as well as a -CN bearing molecule, that is a candidate molecular system to be detected in the interstellar medium (ISM). Our investigation aims to provide direct experimental frequencies of cyanoacetic acid to guide its eventual astronomical search in low-frequency surveys. Using different jet-cooled rotational spectroscopic techniques in the time domain, we have determined a precise set of the relevant rotational spectroscopic constants, including the 14N nuclear quadrupole coupling constants for the two distinct structures, cis- and gauche- cyanoacetic acid. We believe this work will potentially allow the detection of cyanoacetic acid in the interstellar medium, whose rotational features have remained unknown until now.

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

CONTEXT

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)NH2).

AIMS

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.

METHODS

Time-domain Fourier transform microwave (FTMW) spectroscopy under supersonic expansion conditions between 6 GHz and 18 GHz was used to accurately measure and analyze ground-state rotational transitions with resolved hyperfine structure arising from nuclear quadrupole coupling interactions of the 14N nucleus. We combined this technique with the frequency-domain room-temperature millimeter wave and submillimeter wave spectroscopies from 75 GHz to 440 GHz in order to record and assign the rotational spectra in the ground state and in the 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.

RESULTS

We identified and measured more than 5500 distinct frequency lines of propiolamide in the laboratory. These lines were fitted using an effective semi-rigid rotor Hamiltonian with nuclear quadrupole coupling interactions taken into consideration. We obtained accurate sets of spectroscopic parameters for the ground state and the three low-lying excited vibrational states. 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.

CONCLUSIONS

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. The comprehensive spectroscopic data presented in this paper will aid future astronomical searches.

Formation of interstellar cyanoacetamide: a rotational and computational study

CONTEXT

Cyanoacetamide is a -CN bearing molecule that is also an amide derivative target molecule in the interstellar medium.

AIMS

The aim of our investigation is to analyze the feasibility of a plausible formation process of protonated cyanoacetamide under interstellar conditions and to provide direct experimental frequencies of the ground vibrational state of the neutral form in the microwave region in order to enable its eventual identification in the interstellar medium.

METHODS

We used high-level theoretical computations to study the formation process of protonated cyanoacetamide. Furthermore, we employed a high-resolution laser-ablation molecular beam Fourier transform spectroscopic technique to measure the frequencies of the neutral form.

RESULTS

We report the first rotational characterization of cyanoacetamide, and a precise set of the relevant rotational spectroscopic constants have been determined as a first step to identifying the molecule in the interstellar medium. We fully explored the potential energy surface to study a gas-phase reaction on the formation process of protonated cyanoacetamide. We found that an exothermic process with no net activation barrier is initiated by the high-energy isomer of protonated hydroxylamine, which leads to protonated cyanoacetamide.