The chemical species formed in the co-condensation reactions of Pd and Pt atoms with CO at 4.2–10 °K are investigated for the first time using the combined techniques of matrix isolation infrared and laser Raman spectroscopy. Under these experimental conditions the spectroscopic data show that one major product is formed. The data when taken in conjunction with the depolarisation measurements for the matrix isolated species confirms the existence in the matrix of the previously unknown tetracarbonyls Pd(CO)4 and Pt(CO)4 both having Td symmetry. Cotton-Kraihanzel force constants are calculated for the series M(CO)4 where M = Ni, Pd and Pt.