Kinetic isotope effects (KIEs) for the thermal decomposition of N2O catalyzed by chlorine were experimentally determined in the temperature range 773-923 K, and may be expressed as follows : KTE(t)(N-15)=(4100/T-1.90)+/-0.15, KIE(p)(N-15)=(3940/T-2.35)+/-0.10 and KIE(O-18)=(6990/T-3.60)+/-0.25. An Arrhenius fit to the measured rate constants resulted in an activation energy of 136+/-8 kJ mol(-1) and a preexponential factor of 7.7X10(7+/-0.1) m(3) mol(-1) s(-1). The KIEs were interpreted according to the Bigeleisen formalism. Furthermore, we calculated the activation energy following the Sanderson bond-energy-bond-order relationship, and the preexponential factor from transition state theory and compared them to experimental values. Additionally, ab initio molecular theory was employed to study parts of the potential energy surface of the elementary bimolecular reaction between a N2O molecule with a Cl atom. Equilibrium geometries, energies and harmonic vibrational frequencies were calculated at the HF/6-31G* and MP2/6-31G* level for some distinct stationary points on the potential energy surface, with energy refinements at the MP2/6-311G* level. In our study the transition state was located by the eigenvalue-following method. The ab initio properties of the transition state and reactants were also used for an evaluation of the kinetic isotope effects.