The photoion-photoelectron coincidence (PIPECO) spectra for ArCO + in the wavelength region of 620–940 Å have been measured at different nozzle expansion conditions. The ionization energy (IE) for CO +(≈X)·Ar is determined to be 13.33±0.06 eV (930±4 Å). Using this value, the IE for CO +(≈X), and the estimated binding energy for Ar·CO, we calculate a value of 0.70 ± 0.06 eV for the dissociation energy of CO +(X)·Ar. The excited Ar +( 2P J )·CO and CO + (≈A or ≈B)·Ar dimer ions formed by the photoionization of ArCO are found to be dissociative. The dissociation of Ar +( 2P J )·CO is rationalized by a stepwise mechanism involving the formation of a vibrationally excited CO +(≈X,ν′)·Ar complex by near-resonance intramolecular charge transfer and the subsequent dissociation of the complex by vibrational predissociation. Assuming that the radiative lifetimes of CO +(≈A,≈B) and CO +(≈A,≈B)·Ar are identical, we estimate that the dissociation lifetimes of·ar CO +(≈A)·Ar and CO + (≈B)·Ar are shorter than the radiative lifetimes of CO +(≈A) (≈4 μs) and CO +(≈B) (≈50 ns), respectively. The formation of ArCO + and (CO) 2 + from the fragmentation of excited Ar +( 2P J )·(CO) 2 and Ar +( 2P J )·(ArCO) trimer ions is efficient. The good agreement found in the comparison of the measured vibrational distribution of CO +(≈X,ν′) produced in the Ar +( 2P 3 2 )+CO charge transfer reaction and the profile for the ArCO + and (CO) 2 + coincidence electronic bands arisen from the dissociation of Ar +( 2P 3 2 )·(CO) 2 and/ or Ar +( 2P 3 2 )·(ArCO) implies the involvement of near-resonance intramolecular charge transfer between Ar +( 2P 3 2 ) and a CO molecule in the trimer ions prior to their decomposition. Evidence supporting a binding energy for Ar +( 2P 3 2 )·CO to lie in the range of 0.66–0.97 eV is found.