Protonated CO2 in massive star-forming clumps.

Interstellar CO2 is an important reservoir of carbon and oxygen, and one of the major constituents of the icy mantles of dust grains, but it is not observable directly in cold gas because it has no permanent dipole moment. Its protonated form, HOCO+, is believed to be a good proxy for gaseous CO2. However, it has been detected in only a few star-forming regions to date, so its interstellar chemistry is not well understood. We present new detections of HOCO+ lines in 11 high-mass star-forming clumps. Our observations more than treble the number of detections in star-forming regions to date. We derived beam-averaged abundances relative to H2 of between 0.3 and 3.8 × 10−11. We compared these values with the abundances of H13CO+, a possible gas-phase precursor of HOCO+, and of CH3OH, a product of surface chemistry. We found a positive correlation with H13CO+, but no correlation with CH3OH. We suggest that the gas-phase formation route starting from HCO+ plays an important role in the formation of HOCO+, perhaps more important than protonation of CO2 (upon evaporation of CO2 from icy dust mantles). [ABSTRACT FROM AUTHOR]