Combined IRAM andHerschel/HIFI study of cyano(di)acetylene in Orion KL: tentative detection of DC₃N

Abstract

Context. We present a study of cyanoacetylene (HC 3 N) and cyanodiacetylene (HC 5 N) in Orion KL using observations from two line surveys performed with the IRAM 30-m telescope and the HIFI instrument onboard the Herschel telescope. The frequency ranges covered are 80−280 GHz and 480−1906 GHz. Aims. This study (divided by families of molecules) is part of a global analysis of the physical conditions of Orion KL and the molecular abundances in the different components of this cloud. Methods. We modeled the observed lines of HC 3 N, HC 5 N, their isotopologues (including DC 3 N), and vibrational modes using a non-local thermodynamic equilibrium (non-LTE) radiative transfer code. In addition, to investigate the chemical origin of HC 3 N and DC 3 N in Orion KL, we used a time-dependent chemical model. Results. We detect 40 lines of the ground vibrational state of HC 3 N and 68 lines of its 13 C isotopologues. We also detect 297 lines of six vibrational modes of this molecule (ν 7 , 2ν 7 , 3ν 7 , ν 6 , ν 5 , and ν 6 +ν 7 ) and 35 rotational lines of the ground vibrational state of HC 5 N. We report the first tentative detection of DC 3 N in a giant molecular cloud. We have obtained a DC 3 N/HC 3 N abundance ratio of 0.015 ± 0.009, similar to typical D/H ratios of cold dark clouds. We provide column densities for all species and derived isotopic and molecular abundances. We also made a 2 × 2 map around Orion IRc2 and present maps of the HC 3 N lines with energies from 34 to 154 K and of the HC 3 N vibrational modes ν 6 and ν 7 with energies between 354 and 872 K. In addition, a comparison of our results for HC 3 N with those in other clouds has allowed us to derive correlations between the column density, the FWHM, the mass, and the luminosity of the clouds. Conclusions. The high column densities of HC 3 N obtained in the hot core, in particular of the ground vibrational state and the vibrational mode ν 7 , make this molecule an excellent tracer of hot and dense gas. In addition, the wide frequency range covered reveals the need to consider a temperature and density gradient in the hot core to obtain better line fits. The high D/H ratio (similar to that obtained in cold clouds) that we derive suggests a deuterium enrichment. Our chemical models indicate that the possible deuterated HC 3 N in Orion KL is formed during the gas-phase. This fact provides new hints concerning the processes leading to deuteration.

The complexity of Orion: an ALMA view

“…The highest energy vibrationally excited state we can report with confidence is the 6 = 7 = 1 state, at E up ≈ 1170 K and the emission is located near the HC. These are the same states as reported by Esplugues et al (2013) from their single-dish survey. The next states, in the range 1400-1600 K, ( 7 = 4/ 7 = 5 = 1, 4 = 1, and 6 = 2) are possibly seen but not securely detected 3 (Fig.…”

“…We have also detected for the first time in Orion, n-and i-propyl cyanide conformers (C 3 H 7 CN). A few cyanoacetylene (HC 3 N) vibrationally excited transitions are also (probably) detected here for the first time, both for the main isotopologue and for the three singly 13 C substituted isotopologues (some of them have been reported in Esplugues et al 2013, and a contemporary paper published after the submission of the present paper also presents a study of some of these vibrationally excited states; Peng et al 2017). Except for the gGg ethylene glycol isomer, only detected towards IRAS16293 A/B (Jørgensen et al 2016), all the species we present here have been seen in some other massive star forming regions, especially in Sgr B2 (B13 discuss all of these detections concerned with Sgr B2 though some predate that work).…”

“…After the early work by Goldsmith et al (1982Goldsmith et al ( , 1983, who detected the first two vibrationally excited states of cyanoacetylene (HC 3 N, 7 = 1, 2), there were a few further attempts to identify higher excitation levels in this source, and finally the large work of Esplugues et al (2013), which combines IRAM 30 m and Herschel HIFI data, reported numerous excited states (up to 6 = 7 = 1). It can also be noted that vibrationally excited states of numerous other species are now known (e.g.…”

Cometary Isotopic Measurements

“…At low temperatures this has the effect that most 13 C nuclei become incorporated into 13 CO, leading to a relative depletion of 13 C in other interstellar molecules. This can have the secondary consequence that molecules formed on grains should have 12 C/ 13 C ratios similar to that of the accreted CO molecules in their carbonyl or carboxyl functional Blake et al (1987), Turner (1990), Minh et al (1990), Mangum et al (1991), Bergin et al (2010), Esplugues et al (2013), Neill et al (2013). Entry for DNC is from the sample of Fontani et al (2014) groups, whereas other functional groups formed by addition of C atoms should be relatively depleted in 13 C (Charnley et al 2004).…”

Exploring molecular complexity with ALMA (EMoCA): Deuterated complex organic molecules in Sagittarius B2(N2)

“…A few detections or tentative detections of deuterated (complex) organic molecules have been reported toward Orion KL (Gerin et al 1992;Daly et al 2013;Esplugues et al 2013;Neill et al 2013;Coudert et al 2013), but no systematic study of the deuteration of complex organic molecules in high mass star-forming regions has been reported so far.…”