Laser-ablated Au atoms have been co-deposited with CO molecules in solid argon to produce gold carbonyls. in addition to the previously reported Au(CO)(n) (n = 1, 2) and Au-2(CO)(2) molecules, small gold cluster monocarbonyls AunCO (n = 2-5) are formed on sample annealing and characterized using infrared spectroscopy on the basis of the results of the isotopic substitution and CO concentration change and comparison with theoretical predictions. Of particular interest is that the mononuclear gold carbonyls, Au(CO)(n) (n = 1, 2), are favored under the experimental conditions of higher CO concentration and lower laser energy, whereas the yields of the gold cluster carbonyls, AunCO (n = 2-5) and Au-2(CO)(2), remarkably increase with lower CO concentration and higher laser power. Density functional theory (DFT) calculations have been performed on these molecules and the corresponding small naked gold clusters. The identities of these gold carbonyls AunCO (n = 1-5) and Au-n(CO)(2) (n = 1, 2) are confirmed by the good agreement between the experimental and calculated vibrational frequencies, relative absorption intensities, and isotopic shifts.