AbstractThe thermal decomposition of deuterated ethyl chloride CH2DCH2Cl was studied in a static system in the pressure range of 0.1–26 torr, and the Arrhenius expression for the overall decomposition at the high‐pressure limit and in the temperature range of 670–1100 K was found to be\documentclass{article}\pagestyle{empty}\begin{document}$$ k_\infty = 10^{13.33 \pm 0.10} \exp [(- 57,200 \pm 500){\rm cal/mol/}RT]{\rm}s^{- 1} $$\end{document}The intramolecular isotopic effects were first examined in the pressure range of 0.1–26 torr at 837 K, and the branching ratiokH/kDwas found to decrease with increasing pressure. The RRKM‐theory calculations describe the experimental data well.The intramolecular isotopic effect was also examined in the temperature range of 728–926 K, and the branching ratio at the high pressure limit was given by the expression\documentclass{article}\pagestyle{empty}\begin{document}$$ k_{\rm H} /k_{\rm D} = (1.44 \pm 0.05)\exp [(1500 \pm 50){\rm cal/mol/}RT] $$\end{document}whenkHandkDare the rate constants for the HCl and DCl channels of elimination.The ArrheniusAfactors obtained at the high‐pressure limit together with the temperature‐dependent expression of the branching ratio provided additional experimental data for an assignment (fine‐tuned) of the vibrational frequencies of both activated complexes involved in the thermal decomposition of CH2DCH2Cl. The evaluated vibrational frequencies were then used in the RRKM calculations describing the pressure dependence of the intramolecular isotopic effect. The RRKM calculations and the experimental data were in good agreement, supporting the choice of vibrational frequencies for both the activated complexes as well as the trans