A study of the C${}_3$H${}_2$ isomers and isotopologues: first interstellar detection of HDCCC

Abstract

The partially deuterated linear isomer HDCCC of the ubiquitous cyclic carbene ($c$-C${}_3$H${}_2$) was observed in the starless cores TMC-1C and L1544 at 96.9 GHz, and a confirming line was observed in TMC-1 at 19.38 GHz. To aid the identification in these narrow line sources, four centimetre-wave rotational transitions (two in the previously reported $K_a=0$ ladder, and two new ones in the $K_a=1$ ladder), and 23 transitions in the millimetre band between 96 and 272 GHz were measured in high-resolution laboratory spectra. Nine spectroscopic constants in a standard asymmetric top Hamiltonian allow the principal transitions of astronomical interest in the $K_a\le 3$ rotational ladders to be calculated to within 0.1 km s${}^{-1}$ in radial velocity up to 400 GHz. Conclusive evidence for the identification of the two astronomical lines of HDCCC was provided by the $V_{\mathrm{LSR}}$ which is the same as that of the normal isotopic species (H${}_2$CCC) in the three narrow line sources. In these sources, deuterium fractionation in singly substituted H${}_2$CCC (HDCCC/H${}_2$CCC $\sim 4\%\text{-}19\%$) is comparable to that in $c$-C${}_3$H${}_2$ ($c$-C${}_3$H${}_2$/$c$-C${}_3$HD $\sim 5\%\text{-}17\%$), and similarly in doubly deuterated $c$-C${}_3$H${}_2$ ($c$-C${}_3$D${}_2$/$c$-C${}_3$HD $\sim 3\%\text{-}17\%$), implying that the efficiency of the deuteration processes in the H${}_2$CCC and $c$-C${}_3$H${}_2$ isomers are comparable in dark clouds.

Accepted for publication in A&A

References in corpus (8)

• The 2014 KIDA network for interstellar chemistry
• Survey of ortho-H2D+(1_{1,0}-1_{1,1}) in dense cloud cores
• The N2D+/N2H+ ratio as an evolutionary tracer of Class 0 protostars
• The chemistry and spatial distribution of small hydrocarbons in UV-irradiated molecular clouds: the Orion Bar PDR
• Rotational quenching of H2CO by molecular hydrogen: cross-sections, rates, pressure broadening
• Benchmarking spin-state chemistry in starless core models
• Interstellar detection of c-C3D2
• Reactions forming C(0,+)n=2,10, Cn=2,4H(0,+) and C3H(0,+) in the gas phase: semi empirical branching ratios

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