Discovery of interstellar CF+

We discuss the first astronomical detection of the CF+ (fluoromethylidynium) ion, obtained by observations of the (102.6 GHz), (205.2 GHz) and (307.7 GHz) rotational transitions toward the Orion Bar region. Our search for CF+ – carried out using the IRAM 30 m and APEX 12 m telescopes – was motivated by recent theoretical models that predict CF+ abundances of 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 with H2, HF is predicted to be the dominant reservoir of fluorine, not only in well-shielded regions 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 over a region of size , in good agreement with theoretical predictions. They provide support for our current theories of interstellar fluorine chemistry, which suggest that hydrogen fluoride should be ubiquitous in interstellar gas clouds and widely detectable in absorption by future satellite and airborne observatories.