The five-membered, aromatic, heterocyclic compound imidazole (C3N2H4)
was the subject of two unsuccessful searches, by
Dezafra et al. in the 1970s and by
Irvine et al in the 1980s. The earlier search
was made with the old 140 foot telescope telescope
at Green Bank observatory. The later search was made with the
20m millimeter wave telescope at
Onsala Space Observatory in Sweden.