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Measurements of the appearance potentials and the kinetic energies of S + and CS + ions formed by electron impact on carbon disulphide in the gas phase lead us to propose a value as low as 34 ± 6 kcal mole -1 for the heat of formation of the CS radical in its ground electronic state. It is also shown that the predissociations of the A 2 Π u /or X 2 Π g and the B 2 Σ u molecular ion states by a repulsive 4 Σ -state giving rise to S + ions, observed through metastable ions study, occur at 13.45 eV and 14.55 eV respectively.

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The mechanism usually proposed for the pyrolysis of l,2-CzH4Cl2 is discussed in terms of existing data on elementary rate constants and using the value log,,(k,, sec-') = -(20710 k 630)/4.58 T + (14.33 k0.47) measured in this work for the rate constant of the reactionThis discussion is extended to the free-radical pyrolysis of other chlorinated ethanes using recent literature data. The usual Rice-Herzfeld mechanism is questioned in view of the discrepancy between experimental results and values predicted from the knowledge of elementary rate constants of this mechanism.(*) Present address: Solvay Research Center, Neder-over-Heembeek, Brussels. Note added in proofWhile this paper was in the course of publication, a paper by Holbrook, Walker and Watson ( J . Chem. SOC. (B), 577 (1971)) on the pyrolysis of 1,2-dichloroethane was published which leads to similar conclusions. This unstabilized product was kindly supplied by the Solvay Research Center, Nederover-Heembeek, Brussels.