[en] Metastable transitions in the substances CCl₄, C₂Cl₆, SiCl₄ and Si₂Cl₆ have been measured by a double-focusing mass spectrometer. For the most intense transitions, isotope effects as well as relative translational energies of the products have been determined. In all cases, a normal isotope effect was observed. The kinetic isotope effects range from 1.9 in case of a simple Cl elimination from SiCl₄⁺ to values close to 1 in complex molecular elimination processes. For fragmentations where the products consist of non-radical species, a large kinetic release was observed and this is suggested to be due to an energy barrier in the potential energy surface. (auth.)