Electronic Predissociation in the Dichloromethane Cation CH₂Cl₂⁺ Electronic State ²A₁

The loss of a Cl atom from metastable CH₂Cl₂⁺ in the mass-analyzed ion kinetic energy experiment is characterized by a borderline zero kinetic energy release and large kinetic isotope effects on chlorine and hydrogen. Ab initio calculations are employed to assist the interpretation in terms of a nonadiabatic reaction involving electronic predissociation of the electronically excited state ²A₁ and two-dimensional reaction dynamics. Strong curvature in the reaction coordinate leads to a bobsled effect that accounts for the low kinetic energy release. The kinetic isotope effects enter via the predissociation rate and are interpreted in terms of vibrational overlap integrals.