HCO, c-C3H and CF+ : three new molecules in diffuse, translucent and
  "spiral-arm'' clouds
  %methods {We used the EMIR receiver and FTS spectrometer at the IRAM 30m to
construct absorption spectra toward bright extra-galactic background sources at
195 kHz spectral resolution ($\approx$ 0.6 \kms). We used the IRAM Plateau de
Bure interferometer to synthesize absorption spectra of \hthcop\ and HCO toward
the galactic HII region W49.} %results {HCO, \cc3h\ and CF\p\ were detected
toward the blazars \bll\ and 3C111 having \EBV\ = 0.32 and 1.65 mag. HCO was
observed in absorption from ``spiral-arm'' clouds in the galactic plane
occulting W49. The complement of detectable molecular species in the 85 - 110
GHz absorption spectrum of diffuse/translucent gas is now fully determined at
rms noise level $\delta_\tau \approx 0.002$ at \EBV\ = 0.32 mag (\AV\ = 1 mag)
and $\delta_\tau$/\EBV\ $\approx\ 0.003$ mag$^{-1}$ overall.} %conclusions {As
with OH, \hcop\ and \cch, the relative abundance of \cc3h\ varies little
between diffuse and dense molecular gas, with N(\cc3h)/N({\it o-c}-\c3h2)
$\approx$ 0.1. We find N(CF\p)/N(H$^{13}$CO\p) $\approx 5$, N(CF\p)/N(\cch)
$\approx$ 0.005-0.01 and because N(CF\p) increases with \EBV\ and with the
column densities of other molecules we infer that fluorine remains in the gas
phase as HF well beyond \AV\ = 1 mag. We find N(HCO)/N(H$^{13}$CO\p) = 16
toward \bll, 3C111 and the 40 km/s spiral arm cloud toward W49, implying X(HCO)
$\approx 10^{-9}$, about 10 times higher than in dark clouds. The behaviour of
HCO is consistent with previous suggestions that it forms from C\p\ and \HH,
even when \AV\ is well above 1 mag. The survey can be used to place useful
upper limits on some species, for instance N(\hhco)/N(\HH CS) $>$ 32 toward
3C111, compared to 7 toward TMC-1, confirming the possibility of a gas phase
formation route to \hhco.}
