The homogeneous gas-phase pyrolysis of dimethyl mercury has been studied in a wide variety of conditions. The products and kinetic characteristics of the reaction are shown to be more complex than has been supposed. An abridged short-chain radical mechanism which accounts for the main features of the reaction is suggested. Evidence is presented which indicates that the initial unimolecular breakdown of dimethyl mercury is not in its first-order region in the usual range of pressures and temperatures employed and the pressure dependence of the overall first-order rate constant is shown to be in qualitative accord with the predictions of the Kassel-Slater theories. A mechanistic explanation of the so-called type I and type I1 modes of mercury dialkyl decomposition is offered and the experimental conditions for transition of behaviour for dimethyl mercury are stated. The results indicate that the breakdown of the radical *HgCH3 proceeds without measureable activation energy.The experimental conditions in which the pyrolysis of DMM exhibits the characteristics of a homogeneous gas-phase reaction were described in part 1.1 For a detailed study of this reaction a Pyrex vessel (S/Y = 1 cm-1) washed with nitric acid was used. Following exposure to the atmosphere at least six pyrolyses were conducted before measurements were renewed.l The apparatus and experimental procedures employed were as described earlier.1
RESULTS
PYROLYSIS OF DMM ALONEA list of the products of reaction and an indication of their abundance at the extremes of the temperature range employed was given in table 1 of part 1.1 Fig. 1 illustrates a gas chromatogram obtained with the product of the homogeneous decomposition at 440°C of 20 mrn Hg of DMM carried to 5 % reaction. The sample 103
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