Laser-ablated ruthenium or osmium atom reactions with CO and NO mixtures in solid argon produce unsaturated metal carbonyl nitrosyls including M(CO)(NO) and 18-electron configuration M(CO) 2 (NO) 2 molecules (M=Ru, Os). The observed absorption bands of reaction products are identified by isotopic substitution, isotopic ratios and isotopic distributions ( 13 CO, 15 NO, and mixtures). DFT (B3LYP and BP86) vibrational fundamental calculations reproduce observed frequencies and isotopic shifts very well. The bonding and reaction mechanism are discussed.