Discovery of interstellar ketenyl (HCCO), a surprisingly abundant radical^⋆,⋆⋆

¹ Instituto de Ciencia de Materiales de Madrid, CSIC, C/ Sor Juana Inés de la Cruz 3, 28049 Cantoblanco, Spain
e-mail: marcelino.agundez@icmm.csic.es
² Institut de Radioastronomie Millimétrique, 300 rue de la Piscine, 38406 St.-Martin d’Hères, France

Received: 15 April 2015
Accepted: 22 April 2015

Abstract

We conducted radioastronomical observations of 9 dark clouds with the IRAM 30 m telescope. We present the first identification in space of the ketenyl radical (HCCO) toward the starless core Lupus-1A and the molecular cloud L483 and the detection of the related molecules ketene (H₂CCO) and acetaldehyde (CH₃CHO) in these two sources and 3 additional dark clouds. We also report the detection of the formyl radical (HCO) in the 9 targeted sources and of propylene (CH₂CHCH₃) in 4 of the observed sources, which significantly extends the number of dark clouds where these molecules are known to be present. We have derived a beam-averaged column density of HCCO of ~5 × 10¹¹ cm^-2 in both Lupus-1A and L483, which means that the ketenyl radical is just ~10 times less abundant than ketene in these sources. The non-negligible abundance of HCCO found implies that there must be a powerful formation mechanism able to counterbalance the efficient destruction of this radical through reactions with neutral atoms. The column densities derived for HCO, (0.5–2.7) ×10¹² cm^-2, and CH₂CHCH₃, (1.9–4–2) ×10¹³ cm^-2, are remarkably uniform across the sources where these species are detected, confirming their ubiquity in dark clouds. Gas phase chemical models of cold dark clouds can reproduce the observed abundances of HCO, but cannot explain the presence of HCCO in Lupus-1A and L483 and the high abundances derived for propylene. The chemistry of cold dark clouds needs to be revised in light of these new observational results.