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

Context. Glycolamide is a glycine isomer and also one of the simplest derivatives of acetamide (e.g., one hydrogen atom is replaced with a hydroxyl group), which is a known interstellar molecule. Aims. In this context, the aim of our work is to provide direct experimental frequencies of the ground vibrational state of glycolamide in the centimeter-, millimeter- and submillimeter-wavelength regions in order to enable its identification in the interstellar medium. Methods. We employed a battery of state-of-the-art rotational spectroscopic techniques in the frequency and time domain to measure the frequencies of glycolamide. We used the spectral line survey named Exploring Molecular Complexity with ALMA (EMoCA), which was performed toward the star forming region Sgr B2(N) with ALMA to search for glycolamide in space. We also searched for glycolamide toward Sgr B2(N) with the Effelsberg radio telescope. The astronomical spectra were analyzed under the local thermodynamic equilibrium approximation. We used the gas-grain chemical kinetics model MAGICKAL to interpret the results of the astronomical observations. Results. About 1500 transitions have been newly assigned up to 460 GHz to the most stable conformer, and a precise set of spectroscopic constants was determined. Spectral features of glycolamide were then searched for in the prominent hot molecular core Sgr B2(N2). We report the nondetection of glycolamide toward this source with an abundance at least six and five times lower than that of acetamide and glycolaldehyde, respectively. Our astrochemical model suggests that glycolamide may be present in this source at a level just below the upper limit, which was derived from the EMoCA survey. We could also not detect the molecule in the region’s extended molecular envelope, which was probed with the Effelsberg telescope. We find an upper limit to its column density that is similar to the column densities obtained earlier for acetamide and glycolaldehyde with the Green Bank Telescope.

Identification of a vibrationally excited level in methyl formate through microwave and far-infrared spectroscopy

Methyl formate (HCOOCH3) is an important interstellar molecule. More than 1000 rotational transitions including those from the ground state, torsionally excited states, and of its isotopologues have been observed towards several astrophysical sources. The laboratory spectra of methyl formate in the microwave spectral region contain many unassigned transitions and many of them are likely to be due to rotational transitions in the low-lying excited states. We report the laboratory identification of new rotational transitions in the COC deformation (ν12) excited state. The identification was made possible by combining the microwave data with rotation–vibration spectra taken in the far-infrared region at the Canadian Light Source synchrotron.

Rotational spectrum of isotopic methyl mercaptan, 13CH3SH, in the laboratory and towards Sagittarius B2(N2)

Methyl mercaptan (CH3SH) is a known interstellar molecule with abundances high enough that the detection of some of its minor isotopologues is promising. The present study aims to provide accurate spectroscopic parameters for the 13CH3SH isotopologue to facilitate its identification in the interstellar medium at millimetre and submillimetre wavelengths. Through careful analysis of recent CH3SH spectra from 49–510 GHz and 1.1–1.5 THz recorded at natural isotopic composition, extensive assignments were possible not only for the ground torsional state of 13CH3SH, but also in the first and second excited states. The torsion–rotation spectrum displays complex structure due to the large-amplitude internal rotation of the 13CH3 group, similar to the main and other minor isotopic species of methyl mercaptan. The assigned transition frequencies have been fitted to within experimental error with a 52-parameter model employing the RAM36 programme. With predictions based on this fit, 13CH3SH was searched for in spectra from the Atacama Large Millimetre/sub-millimetre Array (ALMA) towards the Galactic centre source Sgr B2(N2). Several transitions were expected to be observable, but all of them turned out to be severely blended with emission from other species, which prevents us from identifying 13CH3SH in this source.

Astrochemical studies at the Cryogenic Storage Ring

The new Cryogenic Storage Ring at the Max Planck Institute for Nuclear Physics (Heidelberg, Germany) has recently become operational. One of the main research areas foreseen for this unique facility is astrochemical studies with cold molecular ions. The spontaneous radiative cooling of the prototype interstellar molecule CH + to its lowest rotational states has been demonstrated by photodissociation spectroscopy, paving the way for experiments under true interstellar conditions. To this end, a low-energy electron cooler and a neutral atom beam set-up for merged beams studies have been constructed. These experiments have the potential to provide energy-resolved rate coefficients for fundamental astrochemical processes involving state-selected molecular ions. The main target reactions include some of the key processes of interstellar chemistry, such as the electron recombination of H 3 + , charge exchange between H 2 + and H, or the formation of CH + in collisions of triatomic hydrogen ions and C atoms. This article is part of a discussion meeting issue ‘Advances in hydrogen molecular ions: H 3 + , H 5 + and beyond’.