Hydrogen-Deuterium Kinetic Isotope Effect at Very High Temperature

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Abstract
The kinetic isotope effect for the reaction CF3+CH2D2→CF3H+CHD2 or CF3D+CH2D has been studied in a shock tube between 1000° and 2000°K where CF3 radicals were produced by thermal decomposition of CF3N2CF3. In the reaction zone gas compositions were: noble gases≫CH2D2≫CF3N2CF3; and in this way ratio of final products CF3H/CF3D was equal to the ratio of rate constants kH/kD. The data are represented empirically by lnkH/kD=ln1.400+0.42×106/T2. A London‐Polanyi‐Eyring‐Sato potential energy surface was constructed, where Sato's parameter was fitted to give the correct activation energy, and the frequencies and zero‐point‐energy of the activated complex were then found from curvatures through the saddle‐point of the potential energy surface. At very high temperatures activated complex theory predicts lnkH/kD=ln1.402+0.502×106/T2 —0.069×1012/T4, in fair agreement with experiment.

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