In 2014, Cernicharo and co-workers reported the tentative detection of the nitrosylium or nitric oxide cation, NO⁺, toward Barnard 1-b, a source making the transition between a dense interstellar cloud and a protostellar system. Only one rotational transition ( J = 2–1 ) was observed. Hyperfine structure that would have strengthened the identification was not resolvable with the observations (made with the IRAM 30m telescope). Subsequently, Rivilla and co-workers reported the same transition toward the galactic core source G+0.693-0.027. The detection will remain tentative until additional confirming transitions are observed.

Since the first ionization energy of O (13.62 eV) is less than that of N (14.53 eV), the bonding in NO⁺ arises from the interaction between N and O⁺. They both have ⁴S ground states and can thus form a triple bond if all the couplings between unpaired electrons on N and O⁺ are formed. NO⁺ is isoelectronic with N₂ and CO (but their dipole moments are all different).