The investigation of the (CO)+2 ion by dissociative ionization of argon/carbon monoxide clusters

The formation of (CO)+2 ion has been investigated by the dissociative ionization of Ar(CO)2 clusters in a threshold photoelectron photoion coincidence experiment. The kinetic energy released (KER) in the reaction Ar(CO)+2→(CO)+2+Ar has been measured as a function of the internal energy of the Ar(CO)+2 ion. The comparison between the experimental KER and the statistically expected KER allows one to extrapolate back to zero KER which corresponds to the thermochemical threshold for the formation of (CO)+2. The ionization potential (IP) of (CO)2 is determined to be 12.24±0.15 eV. This leads to a binding energy of the (CO)+2 of 1.80 eV one of the strongest known for any ionized van der Waals dimer. Our data are in line with a trans planar structure of the CO dimer ion as suggested by our ab initio calculations at the CI level.