Discovery of interstellar ketenyl (HCCO), a surprisingly abundant
  radical
  We have conducted radioastronomical observations of 9 dark clouds with the
IRAM 30m 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 extends significantly
the number of dark clouds where these molecules are known to be present. We
derive a beam-averaged column density of HCCO of 5e11 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)e12 cm-2, and CH2CHCH3, (1.9-4-2)e13
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
the light of these new observational results.
