2015/11/16 by S. Spezzano, H. Gupta, S. Brünken +8 · 1 citation
Physics and Astronomy · #astro-ph.GA
paper · pdf · doi:10.1051/0004-6361/201527460
published as A&A 586, A110 (2016) · Accepted for publication in A&A
arxiv created 2015/11/16 · arxiv updated 2016/02/03
The partially deuterated linear isomer HDCCC of the ubiquitous cyclic carbene (c-C3H2) 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 Ka =0 ladder, and two new ones in the Ka =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 Ka ≤ 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_\rmLSR which is the same as that of the normal isotopic species (H2CCC) in the three narrow line sources. In these sources, deuterium fractionation in singly substituted H2CCC (HDCCC/H2CCC ∼4%-19%) is comparable to that in c-C3H2 (c-C3H2/c-C3HD ∼5%-17%), and similarly in doubly deuterated c-C3H2 (c-C3D2/c-C3HD ∼3%-17%), implying that the efficiency of the deuteration processes in the H2CCC and c-C3H2 isomers are comparable in dark clouds.