We　report　a　photoelectron　spectroscopy　and　density　functional　theory　(DFT)　study　on　the　electronic　and　structural　properties　of　Nb3-,Nb3O-,Nb3O2-,　and　the　corresponding　neutrals.　Well-resolved　photoelectron　spectra　are　obtained　for　the　anion　clusters　at　different　photon　energies　and　are　compared　with　DFT　calculations　to　elucidate　their　structures　and　chemical　bonding.　We　find　that　Nb3-　possesses　a　C2v　(3A2)　structure,　and　Nb3　is　a　scalene　Cs　(2A＇＇)　triangle.　Both　Nb3O-　and　Nb3O　are　found　to　have　C2v　structures,　in　which　the　O　atom　bridges　two　Nb　atoms　in　a　Nb3　triangle.　The　ground-state　of　Nb3O2-　is　found　surprisingly　to　be　a　low　symmetry　C1　(1A)　structure,　which　contains　a　bridging　and　a　terminal　O　atom.　Molecular　orbital　analyses　are　carried　out　to　understand　the　structures　and　bonding　of　the　three　clusters　and　provide　insights　into　the　sequential　oxidation　from　Nb3-　to　Nb3O2-.　The　terminal　Nb=O　unit　is　common　in　niobia　catalysts,　and　the　Nb3O2-　cluster　with　a　Nb=O　unit　may　be　viewed　as　a　molecular　model　for　the　catalytic　sites　or　the　initial　oxidation　of　a　Nb　surface.　©　2009　American　Chemical　Society.