Laser-ablated Mn and Re atoms and electrons react with CO upon co-condensation in excess argon and neon to produce carbonyl neutrals and anions. These species are identified through isotopic substitution, CCl4 doping to trap ablated electrons, and density functional theory isotopic frequency calculations. MnCO is identified at 1933.6 cm(-1) in argon and at 1950.7 cm(-1) in neon, which are in agreement with the gas phase 1955 +/-15 cm(-1) photoelectron measurement. MnCO- is found at 1789.4 cm(-1) in argon and 1807.5 cm(-1) in neon. The Mn(CO)(2) and Re(CO)(2) dicarbonyls are major product absorptions. Annealing to allow further reaction of CO produces higher carbonyls including Mn-2(CO)(10) and Re-2(CO)(10) in solid argon. Argon and neon matrix experiments are compared for both metals.