High-Resolution Infrared Spectroscopy of DC3N in the Stretching Region

The perspectives opened by modern ground-based infrared facilities and the forthcoming James Webb Telescope mission have brought a great attention to the ro-vibrational spectra of simple interstellar molecules. In this view, and because of the lack of accurate spectroscopic data, we have investigated the infrared spectrum of deuterated cyanoacetylene (DC3N), a relevant astrochemical species. The ν1, ν2, and ν3 fundamentals as well as their hot-bands were observed in the stretching region (1,500–3,500 cm−1) by means of a Fourier transform infrared spectrometer. Supplementary measurements were performed at millimeter-wavelengths (243–295 GHz) with a frequency-modulation spectrometer equipped with a furnace, that allowed to probe pure rotational transitions in the investigated stretching states. Furthermore, since HC3N is observed as by-product in our spectra and suffers from the same deficiency of accurate infrared data, its ro-vibrational features have been analyzed as well. The combined analysis of both rotational and ro-vibrational data allowed us to determine precise spectroscopic constants that can be used to model the infrared spectra of DC3N and HC3N. The importance of accurate molecular data for the correct modeling of proto-planetary disks and exoplanetary atmospheres is then discussed.

Spectroscopic evidence of the C–N covalent bond formed between two interstellar molecules (ISM): acrylonitrile and ammonia

A new CN covalent bond was formed between acrylonitrile and ammonia in ionization state.

Search for H3+ isotopologues toward CRL 2136 IRS 1

Context. Deuterated interstellar molecules frequently have abundances relative to their main isotopologues much higher than the overall elemental D-to-H ratio in the cold dense interstellar medium. H3+ and its isotopologues play a key role in the deuterium fractionation; however, the abundances of these isotopologues have not been measured empirically with respect to H3+ to date. Aims. Our aim was to constrain the relative abundances of H2D+ and D3+ in the cold outer envelope of the hot core CRL 2136 IRS 1. Methods. We carried out three observations targeting H3+ and its isotopologues using the spectrographs CRIRES at the VLT, iSHELL at IRTF, and EXES on board SOFIA. In addition, the CO overtone band at 2.3 μm was observed by iSHELL to characterize the gas on the line of sight. Results. The H3+ ion was detected toward CRL 2136 IRS 1 as in previous observations. Spectroscopy of lines of H2D+ and D3+ resulted in non-detections. The 3σ upper limits of N(H2D+)/N(H3+) and N(D3+)/N(H3+) are 0.24 and 0.13, respectively. The population diagram for CO is reproduced by two components of warm gas with the temperatures 58 and 530 K, assuming a local thermodynamic equilibrium (LTE) distribution of the rotational levels. Cold gas (<20 K) makes only a minor contribution to the CO molecular column toward CRL 2136 IRS 1. Conclusions. The critical conditions for deuterium fractionation in a dense cloud are low temperature and CO depletion. Given the revised cloud properties, it is no surprise that H3+ isotopologues are not detected toward CRL 2136 IRS 1. The result is consistent with our current understanding of how deuterium fractionation proceeds.

Laboratory spectroscopic study of the 15N isotopomers of cyanamide, H2NCN, and a search for them toward IRAS 16293−2422 B

Context. Cyanamide is one of the few interstellar molecules containing two chemically different N atoms. It was detected recently toward the solar-type protostar IRAS 16293−2422 B together with H2N13CN and HDNCN in the course of the Atacama Large Millimeter/submillimeter Array (ALMA) Protostellar Interferometric Line Survey (PILS). The detection of the 15N isotopomers or the determination of upper limits to their column densities was hampered by the lack of accurate laboratory data at the frequencies of the survey. Aims. We wanted to determine spectroscopic parameters of the 15N isotopomers of cyanamide that are accurate enough for predictions well into the submillimeter region and to search for them in the PILS data. Methods. We investigated the laboratory rotational spectra of H215NCN and H2NC15N in the selected region between 192 and 507 GHz employing a cyanamide sample in natural isotopic composition. Additionally, we recorded transitions of H2N13CN. Results. We obtained new or improved spectroscopic parameters for the three isotopic species. Neither of the 15N isotopomers of cyanamide were detected unambiguously in the PILS data. Two relatively clean lines can be tentatively assigned to H215NCN. If confirmed, their column densities would imply a low 14N/15N ratio for cyanamide toward this source. Conclusions. The resulting line lists should be accurate enough for observations up to about 1 THz. More sensitive observations, potentially at different frequencies, may eventually lead to the astronomical detection of these isotopic species.

Infrared intensities and molar refraction of amorphous dimethyl carbonate – comparisons to four interstellar molecules

The first measurements of infrared (IR) band intensities of solid dimethyl carbonate are presented along with measurements of this compound's refractive index and density near 15 K, neither of which has been reported.