Giant chlorine isotope effect of ion-molecule reaction

Isotope substitution profoundly influences chemical reactions, signifying different reaction rates due to mass-related nuclear quantum effects. Due to the smaller mass-difference ratio, heavy-atom isotope effect is usually much weaker than the hydrogen/deuterium effect, which has been the underlying principle for chemical isotope labelling, a prevailing technique of environmental assessments. Here we report a giant chlorine ( ^35,37 Cl) isotope effect of the collisional reactions between iso -dichloroethylene (naturally comprising ^35,37 Cl-isotopologues) and argon ion. As a grave challenge to conventional understandings, we find that the isotopic signature δ ³⁷ Cl of the dehydrochlorination channel is one thousand times larger than the regular values, namely, an extraordinary priority of the product C ₂ H ³⁷ Cl ⁺ . Hydrogen-atom scrambling and roaming assisted ³⁵ Cl-elimination mechanisms are proposed for this unprecedentedly strong isotope effect. Our finding adds a new dimension of isotope effects and enlightens related methodological renovations of environmental assessment.