Abstract
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.
Highlights
Interstellar DC3N was first discovered in the dark cloud TMC-1 (Taurus Molecular Cloud 1) through the observation in emission of its J 5 − 4 rotational transition lying at nearly 42.2 GHz (Langer et al, 1980)
To fill the lack of information described above, in this work we report on a comprehensive investigation of the high-resolution MIR spectra of DC3N and HC3N, obtained using Fouriertransform infrared (FTIR) spectroscopy
We focus on the fundamental transitions of the ]1, ]2, and ]3 stretching modes, and their hot bands (]1 + ]7 − ]7, ]2 + ]7 − ]7, and ]3 + ]7 − ]7), which all lie in the MIR region
Summary
Interstellar DC3N was first discovered in the dark cloud TMC-1 (Taurus Molecular Cloud 1) through the observation in emission of its J 5 − 4 rotational transition lying at nearly 42.2 GHz (Langer et al, 1980). The MidInfrared Instrument (MIRI) covers continuously the 5–28 μm region at mid resolution (R ∼ 3, 000) with four bands (Banks et al, 2008), while NIRSPEC is designed to pinpoint the shorter wavelength range (1.8–5.2 μm) Such facilities will provide a full spectral overview of the sources, allowing to sample simultaneously the complete vibrational manifold of the molecular targets: i.e., the bending region below 12 μm already excited in the warm gas (T < 500 K), and the C-H stretching region around 3 μm, characterised by high excitation energies (E/k ∼ 4, 000 K) and useful to probe the inner (AU-sized) parts of proto-planetary disks and the atmospheres of hot exoplanets. The analysis of DC3N provides a highly-precise rest-frequency catalog useful for astronomical observations
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