The detection of iron monoxide (FeO) toward Sgr B2 was reported by Walmsley et al. in 2002 using the IRAM 30m telescope. A follow-up study by Furuya et al. in 2003 confirmed the detection of the line at 153.135 GHz reported in the initial study, but the detection will remain tentative until other rotational lines associated with FeO can be identified.

Diatomic FeO bears little resemblance to the mineral iron (II) oxide, which shares the same chemical formula. Diatomic FeO has (Fe⁺)(O^–) ionic character but also involves a weak sigma bond between the 3dz² orbital on Fe and the 2pz orbital on O.

These two orbitals are coupled together in the GVB wavefunction to form a sigma bond. There are also four singly occupied 4s and 3d orbitals.
		Fe 3dz2	O 2pz