15N and 18O kinetic isotope effects in the thermal decomposition of N2O catalyzed by bromine

Abstract

15N and 18O kinetic isotope effects (KIEs) in the thermal decomposition of N2O catalyzed by bromine were experimentally determined in the temperature range 773–873 K, resulting in KIE (15N)=−2.07+4020/T and KIE (18O)=−0.41+3290/T. For theoretical interpretation, based on the Bigeleisen formalism, the following planar transition states were taken into account: trans (N–N–O–Br)‡, trans (Br–N–N–O)‡, and branched (N–N<OBr)‡. In addition to KIE, activation energy according to the Sanderson bond-energy–bond-order relationship and pre-exponential factor were calculated as subsidiary parameters in selecting an appropriate transition state among all probable configurations. The result reveals that it is meaningless to speculate whether the Br atom approaches the central or the terminal N atom of the N2O molecule, since both transition states could generate acceptable values of the kinetic isotope effects, activation energy, and pre-exponential factor.