The ground geometries of Mo(CO)~n^+(n=1～6) compounds were studied by using DFT/B3LYP method. The structure and ground state of each fragment ion are C~∞~ν(^6∑^+), D~∞~h(^6∑~g^+), C~2~υ(^2A~2) or D~3~h(^6A~1), D~4~H(^4A~1~g), C~2~ν(^2B~2) or C~4~ν'(^2B~1), and D~3~d(^2A~1~g) for n=6 sequentially. The results indicate that the geometry of each species (n≥3) is sensitive to the spin state. the sequential bond dissociation energies (D~0) for CO－Mo (CO)~n~-~1^+ are also calculated, and the results are in good agreement with the experiment, while the D~0 for n=3 is too small. The D~0 values varied nonmonotonically with the number of ligands were discussed in term of 5s4d hybridization of Mo atom. In addition, the relations between the number of CO and the stability of fragment ions were discussed by analyzing the spin multiplicities of the system.

Key words: MOLYBDENUM COMPOUNDS, CARBONYL COMPOUNDS, DISSOCIATION, MOLECULAR ORBITAL THEORY