Discovery of interstellar CF

We discuss the first astronomical detection of the CF + (fluoromethylidynium) ion, obtained by observations of the J = 1− 0 (102.6 GHz), J = 2− 1 (205.2 GHz) and J = 3− 2 (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF + - carried out using the IRAM 30m and APEX 12m telescopes - was motivated by recent theoretical models that predict CF + abundances of few× 10 −10 in UV-irradiated molecular regions where C + is present. The CF + ion is produced by exothermic reactions of C + with HF. Because fluorine atoms can react exothermically wit h H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded re gions but also in the surface layers of molecular clouds where the C + abundance is large. The observed CF + line intensities imply the presence of CF + column densities≥ 10 12 cm −2 over a region of size > ∼ 1 ' , in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride sho uld be ubiquitous in interstellar gas clouds and widely detectable in absorption by future satellite and airborne observatori es.