Laser-ablated manganese atoms react with CO and NO mixtures upon condensation in excess argon and further annealing to produce a series of unsaturated manganese carbonyl nitrosyl complexes including Mn-(CO)(NO), Mn(CO)(NO)(2), and Mn(CO)(2)(NO). The Mn(CO)(NO) complex isomerizes to Mn(CO)(eta(2)-NO) on visible photolysis, which rearranges to the isocyanate OMnNCO molecule on ultraviolet photolysis. The Mn(CO)(NO)(eta(2)-NO) and Mn(CO)(NO)(2)(eta(2)-NO) isomers also appear on annealing as does Mn(CO)(4)(NO). The major product after annealing is the stable 18-electron molecule Mn(CO)(NO)(3). The observed absorption bands of reaction products were identified by isotopic substitution ((CO)-C-13-O-16, (NO)-N-15-O-16, (NO)-N-15-O-18, and mixtures) and reproduced within 1-3% by density functional theory calculations of vibrational fundamentals. The bonding and reaction mechanisms are discussed. The isocyanate species formed here from the simple Mn(CO)(NO) complex is relevant to catalytic reactions for pollution control.