The dissociation energy of Cl2O2+

Crystal structures containing a trapezoidal Cl2O2+ cation, one of several structural isomers of Cl2O2+, have been recently obtained by the Seppelt group. There is no experimental thermochemistry for this isomer, partly because the corresponding neutral structure has no significant interdiatomic bonding. We have measured the 0 K dissociation energy D(Cl2+O2) = 57 ± 7 kJ/mol using energy resolved collision-induced dissociation experiments in a flowing afterglow-tandem mass spectrometer. This leads to ΔfH298(Cl2O2+) = 1056 ± 7 kJ/mol. The calculated B3LYP/aug-cc-pVTZ dissociation energy is 13 kJ/mol higher than experiment, while CASPT2 calculations by Seppelt and coworkers give a result 8 kJ/mol below experiment. The agreement between experiment and theory is better than for the related X4+ (X = Cl, Br, and I) cations.