ISOMERIZATION AND DECOMPOSITION OF CHLOROMETHYLACETYLENE

The isomerization and thermal decomposition of chloromethylacetylene ( CMA) has been studied with two shock tube techniques. The first experi ment (Jerusalem) utilizes single-pulse shock tube methods to measure t he isomerization rate of CMA to chloroallene. In addition, equilibrium constants can be estimated at similar to 1200 K. The second experimen t (Argonne) monitors Cl-atom formation at temperatures above similar t o 1150 K. Absolute yield measurements have been performed over the 120 0-1700 K range and indicate that two decomposition channels contribute to CMA destruction, namely, Cl fission and HCl elimination. The resul ts show that the branching fraction between processes is temperature d ependent. Therefore, direct Cl-atom fission is accompanied by molecula r elimination, undoubtedly giving HCl and one or more isomers of C3H2. MP2 6-31G(d,p) ab initio electronic structure calculations have been used to determine vibration frequencies and moments of inertia for thr ee C3H3Cl isomers. Using these quantities, the experimental equilibriu m constants required that Delta H-0(0)(CH2Cl-C=CH reversible arrow CHC l=C=CH2) = -0.24 kcal mole(-1). A potential energy. surface pertinent to the present system has been constructed, and RRKM calculations have been carried out in order to explain the isomerization rates. The iso merization data can be explained with E(0) = 52.3 kcal mole(-1) and [D elta E(down)] = 225 cm(-1). Subsequent semi-empirical Tree and RRKM-Go rin modeling of the Cl atom rate data require E(0) = (67.5 +/- 0.5) kc al mole(-1) with a [Delta E(down)] = (365 +/- 90) cm(-1). This suggest s a heat of formation for propargyl radicals of (79.0 +/- 2.5) kcal mo le(-1).