Fluoronium (protonated hydrogen fluoride, H₂F⁺) was the subject of an unsuccessful search with the Atacama Large Millimeter/submillimeter Array (ALMA) reported in 2016 by Kawaguchi et al. The compound was sought toward the extragalactic blazar PKS 1830-211 with ALMA. It was also sought using the Herschel Space Observatory toward galactic sources NGC 6334 I and W51C. Hydrogen fluoride was detected toward PKS 1830-211 by the study. The search for fluoronium was made possible by laboratory rotational spectra by Fujimori et al. and Amano et al. reported in 2011 and 2012, respectively.

Fluoronium resembles water. Both are asymmetric tops with complex rotational spectra. The analogous halogen compound chloronium (H₂Cl⁺) was initially detected in 2010 and then subsequently observed toward PKS 1830-211 by Muller et al. In spite of its exotic character, fluoronium has been found to play a role in certain organic chemistry syntheses studied in the laboratory.