Laser-ablated iron atoms have been reacted with CO molecules during condensation in excess argon. The FeCO molecule is observed at 1922.0 cm(-1) in solid argon based on concentration studies, isotopic shifts, and density functional theory frequency calculations; the argon matrix redshifts this band 27.0 cm(-1) (1.4%) from the high-resolution gas phase measurement. Absorptions at 1879.2 and 1984.8 cm(-1) are assigned from isotopic substitution and density functional theory frequency calculations to the antisymmetric and symmetric vibrations of a bent Fe(CO)(2) molecule in the matrix. The Fe(CO)(x) (x = 3,4,5) molecules are also observed on annealing in agreement with earlier matrix work. Iron carbonyl ions were also produced and trapped: photosensitive absorptions at 1770.3, 1721.9, 1815.0, 1786.5, and 1853.5 cm(-1) are assigned to FeCO-, Fe(CO)(2)(-), Fe(CO)(3)(-), and Fe(CO)(4)(-), respectively, and a weak photosensitive 2081.5 cm(-1) band is assigned to FeCO+ Polynuclear metal carbonyls were also formed on annealing; based on different CO concentration and laser power experiments and isotopic substitution, an 1897.7 cm(-1) absorption is assigned to Fe2CO and a 1948.5 cm(-1) band to Fe3CO.