A search for CO^+ in planetary nebulae

We have carried out a systematic search for the molecular ion CO^+ in a sample of eight protoplanetary and planetary nebulae in order to determine the origin of the unexpectedly strong HCO^+ emission previously detected in these sources. An understanding of the HCO^+ chemistry may provide direct clues for the physical and chemical evolution of planetary nebulae. We find that the integrated intensity of the CO^+ line may be correlated with that of HCO^+, suggesting that the reaction of CO^+ with molecular hydrogen may be an important formation route for HCO^+ in these planetary nebulae