The co-condensation reaction of atomic palladium with a dilute CO–argon mixture (1:1000) at 10°K yields intermediate carbonyls of palladium Pd(CO)n where n = 1–3 as well as very small amounts of Pd(CO)4. Isotopic substitution experiments using 12C18O were used to aid the spectral assignments. The probabilities of forming the various Pd(CO)n carbonyl species as a function of the CO concentration in Ar are analyzed and compared with the experimental observations. An analysis of the diffusion kinetics demonstrates their usefulness in assigning bands to various species in a series of compounds such as Pd(CO)n. The data make possible the assignment of infrared absorptions at 2070, 2060, 2044, and 2050 cm-1 to tetrahedral (Td) Pd(CO)4, trigonal planar (D3h) Pd(CO)3, linear (D8h) Pd(CO)2 and linear (C8v) PdCO, respectively. Cotton–Kraihanzel force constants are calculated for Pd(CO)n and are compared with those for the analogous intermediate carbonyls of nickel, Ni(CO)n.