September 2007


In 1970, Buhl & Snyder reported a radio line at 89.190 GHZ that they observed in a number of objects, including W3(OH), Orion, L134, W51, and an ammonia cloud near Sgr A. With no solid spectroscopic data available for an assignment, they dubbed the carrier X-ogen. Although Klemperer suggested that protonated carbon monoxide, HCO+, might be the carrier, confirmation was delayed until 1975, when Woods et al. observed the line in the laboratory. While the subsequent observation of the 13C isotope by Snyder et al. provided further evidence, another rotational line of HCO+ was not reported until the 1979 work of Huggins et al.. HCO+ and two of its isotopomers have also been detected in extragalactic sources.

HCO+ (also known as the formyl cation) can be formed by the proton transfer from H3+ to CO and by other pathways. While HCO+ is more stable, the proton can also be added to the other end of CO to form HOC+, which has also been detected.

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