The gas-phase, ion molecule reaction between C,O:' and C,O, has been studied by both double-focusing and ion trap mass spectrometry, rationalized by the formation of a dimeric, odd electron cation IC6041+" which decomposes extensively through sequential CO losses giving rise to IC,O,l+. and IC,O,l+' ions. The thermodynamics of this process have been investigated by means of ab initio calculation performed on the above species using different basis sets (STO-3G, 3-21G and 6-31G*).t Present address: