The ionic fragments formed by collision-induced dissociation of Mn2(CO) + ions (y=1–10) are reported. The ratio of product ions formed by metal-metal vs. metal-ligand bond cleavage are discussed in terms of the dependence of the metal-metal bond energy on the metal-to-ligand ratio. The collision-induced dissociation data indicate that the metal-metal bond energy of Mn2(CO) 5 + and Mn2(CO) 10 + is less than that for Mn2(CO) + (y=1–4 and 6–9). The product ions arising by metal-metal and metal-ligand bond cleavage reactions for collision-induced dissociation and photodissociation are compared. On the basis of this data and the known photochemistry/photophysics of Mn2(CO)10, it is proposed that the difference in collision-induced dissociation and photodissociation product ion branching ratios is attributable to spin-orbit transitions of the activated ions.