HOCO⁺ is an example of an astromolecular ion. Its detection was reported in 1981 by Thaddeus, Guélin, and Linke. HOCO⁺ consists of CO₂ with H⁺ attached to one of the oxygen atoms, hence the designation "protonated carbon dioxide." A number of charged astromolecules are protonated forms of common neutral species and are natural precursors for them. A common reaction in the interstellar medium involves capture of a free electron by a cationic species, known as dissociative recombination:

HOCO⁺ + e^- → CO₂ + H

Interestingly, HOCO⁺ was detected in the interstellar medium before CO₂. Carbon dioxide is harder to detect because its ground electronic state has a zero dipole moment, which results in only weak IR and millimeter features. HOCO⁺ is a quasilinear molecular ion, a nearly symmetric top, which is isolectronic with HNCO HNCO (isocyanic acid) and HOCN) cyanic acid.