Symmetry induced kinetic isotope effects in the formation of Ar⋅CO+2

Symmetry induced kinetic isotope effects (SIKIE) have been observed mass spectrometrically in the termolecular association reaction of Ar and CO+2 to produce Ar⋅CO+2 making this the first example of SIKIE in a system where the reactants have no atoms in common. The 18O SIKIE shows a pronounced dependence on whether the CO+2 are produced directly by electron ionization or indirectly by charge transfer from Ar+. The results can be understood generally in terms of reaction restrictions based on a symmetry correlation scheme recently developed by one of the authors. This scheme indicates that CO+2 ions can have very different clustering reactivity with Ar depending on whether the ion is in an e (restricted) or an f (allowed) parity label state. Kinetic modeling of the 18O SIKIE indicates that CO+2(e)/CO+2(f )≊60 for CO+2 produced by 21 eV electron ionization.