Shock Wave Study of the Thermal Dissociations of C3F6and c-C3F6. I. Dissociationof Hexafluoropropene.

Thethermal dissociation of C3F6was studiedbetween 1330 and 2210 K in shock waves monitoring the UV absorptionof CF2. CF2yields of about 2.6 per parent C3F6were obtained at reactant concentrations of500–1000 ppm in the bath gas Ar. These yields dropped to about1.8 when reactant concentrations were lowered to 60 ppm. The increaseof the CF2yield with increasing concentration was attributedto bimolecular reactions between primary and secondary dissociationproducts. Quantum-chemical and kinetic modeling calculations helpedto estimate the contributions from the various primary dissociationsteps. It was shown that the measurements correspond to unimolecularreactions in their falloff range. Falloff representations of the rateconstants are given, leading to an overall high pressure rate constant k∞= 2.0 × 1017(−104kcal mol–1/RT) s–1and a relative rate of about 2/3:1/3 for the reactions C3F6→ CF3CF + CF2versus C3F6→ C2F3+ CF3. [ABSTRACT FROM AUTHOR]