Aluminium(II) oxide or aluminium monoxide is a compound of aluminium and oxygen with the chemical formula AlO. It has been detected in the gas phase after explosion of aluminized grenades in the upper atmosphere[1][2][3] and in stellar absorption spectra.[4]
Aluminium(II) oxide is one of the aluminium oxides (the most common is Aluminium oxide Al2O3), as it was the rare example of aluminium(II) compound since aluminium usually exists in its +3 oxidation state.
^Merrill, P. W.; Deutsch, A. J. & Keenan, P. C. (1962). "Absorption Spectra of M-Type Mira Variables". Astrophysical Journal. 136: 21. Bibcode:1962ApJ...136...21M. doi:10.1086/147348.