The formation of ArCO+ ions has been investigated in a photoelectron photoion coincidence experiment by dissociative ionization of Ar2CO clusters. The kinetic energy released (KER) in this dissociation has been measured as a function of the internal energy of the parent cluster ion and compared to the KER expected on the basis of statistical theory of unimolecular reaction, e.g., phase space theory. The latter calculations are based on high level ab initio calculations of the ArCO+ ion and the Ar2CO+ ion. The ab initio calculations show a nonlinear equilibrium geometry of the ArCO+ ion. The comparison of experimental and theoretical KER leads to an adiabatic ionization potential of the ArCO of 13.03 eV and a dissociation energy of the ArCO+ ion of 1.00 eV. (C) 1997 American Institute of Physics. [S0021-9606(97)02041-2].