Isotope effect in isotope-exchange reactions: evidence for a large 12C/13C kinetic isotope effect in the gas phase

The O-exchange reaction between CO2+ and CO is triggered by two different entrance channels in 13C-labeled systems. The unimolecular dissociation of the C13CO3+ reactive intermediate is investigated at varying energies by mass spectrometric techniques. An almost “one-way” O-exchange at energies close to the dissociation threshold discloses a remarkably large intramolecular 12C/13C kinetic isotope effect ranging from 6.0 to 7.3 ± 0.5