Extensive ro-vibrational analysis of deuterated-cyanoacetylene (DC3N) from millimeter-wavelengths to the infrared domain

Abstract

Cyanoacetylene, the simplest cyanopolyyne, is an abundant interstellar molecule commonly observed in a vast variety of astronomical sources. Despite its importance as a potential tracer of the evolution of starforming processes, the deuterated form of cyanoacetylene is less observed and less studied in the laboratory than the main isotopologue. Here, we report the most extensive spectroscopic characterization of DC 3 N to date, from the millimeter domain to the infrared region. Rotational and ro-vibrational spectra have been recorded using millimeter-wave frequency-modulation and Fourier-transform infrared spectrometers, respectively. All the vibrational states with energy up to 1015 cm −1 have been analyzed in a combined fit, where the effects due to anharmonic resonances have been adequately accounted for. The analysis contains over 6500 distinct transition frequencies, from which all the vibrational energies have been determined with good precision for many fundamental, overtone, and combination states. This work provides a comprehensive line catalog for astronomical observations of DC 3 N.

High-Resolution Infrared Spectroscopy of DC3N in the Stretching Region

“…The inclusion of rotational lines, whose precision is intrinsically much higher than ro-vibrational data, led to an improved determination of the upper state spectroscopic parameters. If compared to the previous work, our constants are more than two orders of magnitude more accurate than those from Mallinson and Fayt (1976), and are consistent with the most recent spectroscopic data available for DC 3 N (Melosso et al, 2020) and HC 3 N (Bizzocchi et al, 2017). Additionally, the line list for the ] 2 + ] 7 − ] 7 hot-band reported by Mallinson and Fayt (1976) in their Supplementary Material appears to be wrong and inconsistent with the spectroscopic constants they reported in the paper.…”

“…DC 3 N is a closed shell linear molecule which possesses seven vibrational modes: four stretching modes (v 1 , v 2 , v 3 , v 4 ; symmetry) and three doubly-degenerate bending modes (v 5 , v 6 , v 7 ; symmetry), all of being infrared-active. The lowlying vibrational states (v 4 , v 5 , v 6 , v 7 ) as well as some of their overtone and combination states have been extensively analyzed in a previous paper (Melosso et al, 2020). In the present work, we focus on the fundamental transitions of the ] 1 , ] 2 , and ] 3 stretching modes, and their hot bands (]…”

“…The upper states spectroscopic parameters determined from the combined analysis of rotational and rovibrational transitions are collected in Table 2. The spectroscopic constants of the ground and v 7 1 states, i.e., the lower levels involved in the current analysis, were kept fixed at the values determined in our previous global analysis (see Tables 4, 5 in Melosso et al, 2020).…”

“…Unit a Fixed at the v7 1 value (Melosso et al, 2020). b Fixed at the ground state value (Melosso et al, 2020).…”

“…The laboratory spectroscopic knowledge of DC 3 N over the full spectral range of interest for astronomy is, however, not homogeneous. While the rotational spectrum of DC 3 N has been accurately studied and it is well suited to guide astronomical observations at millimeter wavelengths, a detailed knowledge of its infrared spectrum is limited to the spectral range between 200 and 1,100 cm −1 (Melosso et al, 2020). At higher frequencies, only low-accuracy spectroscopic data are available in the literature (Mallinson and Fayt, 1976).…”