Trioxidonitrogen(•) or nitrate radical is an oxide of nitrogen with formula NO3, consisting of three oxygen atoms covalently bound to a nitrogen atom. This highly unstable blue compound has not been isolated in pure form, but can be generated and observed as a short-lived component of gas, liquid, or solid systems. Like nitrogen dioxide NO2, it is a radical (a molecule with an unpaired valence electron), which makes it paramagnetic. It is the uncharged counterpart of the nitrate anion NO−3 and an isomer of the OONO.