Publication costs borne completely by The Journal of Physical ChemietryThe thermal decomposition of l,l,l-trifluoroethane has been investigated in a single-pulse shock tube between 1080 and 1310°K at total reflected shock pressures from -2400 to 3400 Torr. Under these conditions, the mode of decomposition consists almost exclusively of the unimolecular elimination of hydrogen fluoride, CHaC FB -* CH2CFz + HF. The first-order rate conkant is given by log (ICl, sec-l) = 14.0 f 0.4 -. (68.7 * 2.4 kcal)/ 2.303RT. Relative to ethyl fluoride and 1,l-difluoroethane the activation energy for the dehydrofluorination reaction increases significantly with increased fluorine substitution at the a-carbon position. As a comparative study the dehydrochlorination of ethyl chloride has been carried out in the temperature range 990 to 1200°K.The ,4rrhenius parameters for this reaction were found to be log (A, sec-I) = 13.6 * 0.4 and E,,t = 55.8 * 1.9 kloal mol-' in satisfactory agreement with previous literature values. kl

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The thermal decomposition of perfluorocyclobutane was studied between 1100 and 1265°K behind reflected shock waves in a modified single-pulse shock tube using dilute c-CaFg-Ar mixtures. Reflected shock temperatures were evaluated from the Rankine-Hugoniot equations using measured incident and reflected shock velocities. Analyses were carried out by mass spectrometry and gas chromatography. The observed reaction product was almost exclusively CzF4 except at the highest temperatures where small amounts of C3Fa were also observed. The principal process involves the unimolecular decomposition, c -C~F~ -+ 2CzF4. The first-order highpressure rate constant was found to be k" = 1016.0*o.6 exp[(-75,500 f 3000)/RT]sec-1 in good agreement with previous low temperature data obtained in a static system.

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