1194
A. P. MODICA
Chemical Kinetics of Carbonyl Fluoride Decomposition in Shock Waves1
by A. P. Modica Avco Corporatwn, Wilmington, Massachusetts 01887
(Received February go, 1969)
An infrared technique has been used to monitor the thermal decomposition of carbonyl fluoride (COF2) in argon and nitrogen diluent behind incident and reflected shock waves. Data were taken in the temperature range 2200 to 3600°K at total pressures between 0.2 and 26 atm. Direct sampling of reflected shock mixtures with a time-of-flight mass spectrometer provided knowledge of the decomposition products. The pressure and temperature dependence of the COFz dissociation rate constants are discussed in terms of the RiceRamsperger-Kassel unimolecular theory. Rate constants for the fluorine extraction reactions and COF disproportionation reaction were obtained by curve fitting the complete COF2 kinetic histories with computed profiles. A chemical nonequilibrium stream-tube program which includes wall boundary layer effects was used for data analysis.
Introduction Presently, the chemical rates for fluorocarbon decomposition and oxidation kinetics are needed for input to a number of aerospace engineering problems. Mass spectrometer study on the pyrolysis of Teflon plastic (polytetrafluoroethylene) in atmospheres of air and oxygen2 shows that carbonyl fluoride (COF ) IS ’ an important low-temperature (800°K) oxidation intermediate, and. that a t higher temperatures carbon dioxide (COZ) and perfluoromethane (CFJ dominate the reaction products. Measurements to identify the infrared and visible spectrum of an air-Teflon boundary layer in a hot subsonic arc jet have shown the presence of the CN violet and red bands and structure in the 2- to 6-p region characteristic of the COFZ, CO, and C02 molecular b a n d ~ . 3 & Single-pulse *~ shock-tube experiments of the tetrafluoroethylene oxidation in the range 1200 to 2000°K show product distributions of COF2, CO, CFA, C2FsJ and small amounts of C3Fe and C02.4 I n a shock-tube study of the difluoromethylene-oxygen reaction, infrared measurements have directly identified COFz as the initial oxidation product of these reactants. Preliminary results show that at temperatures
constitutes the major primary step and that the elimination of one hydrogen atom from each carbon atom
+ H2
CHa.CH3-%- CH2:CH2
(b)
is a much less important process. In these studies it appears that the primary formation of ethyl radicals and hydrogen atoms as originally proposed by Wijnen6 prove to have little significance. However, in the CHa-CH,
CzH6
+H
(c)
mercury *PI sensitized decomposition of ethane16primary step (c) appears to be the important reaction. T h e JOUTnal of Physical Chemistry
In the continuous irradiation technique which has previously been used in the investigation of the ethane decomposition, it is possible that secondary reaction of the products might obscure the importance of (c). The end product analysis in flash photolysis, where the combination reaction of radicals may become more significant than in the low-intensity photolysis, is performed to reexamine the direct decomposition of ethane.
Experimental Section The sketch and the detailed construction of the flash lamp used in this investigation have been described elsewhere.’ Argon, krypton, or xenon at a pressure of
(1) (a) Supported in part by the U.5 . Atomic Energy Commission. Presented a t the 153rd National Meeting of the American Chemical Society, Miami Beach, Fla., April 10-14, 1967. (b) Department of Chemistry, University of Minnesota, Morris, Minn. 56267. (2) “Advances in Photochemistry,” W. A. Noyes, Jr., G. 8. Hammond, and J. N. Pitts, Jr., Ed., John Wiley & Sons, New York, N. Y.,Vol. 3,1964,p 204. (3) (a) See ref 2, page 210; (b) J. R. McNesby, et al., J. Chem. Phys., 40, 1099 (1964); (c) T.Tanaka et al., ibid., 42, 3864 (1965); (d) D.R. Crosley, ibid., 47,1351(1967). (4) H.Okabe, J. O p t . SOC. Amer., 54,478 (1964). (5) M. H.J. Wijnen, J . Chem. Phys.,24,851 (1956). (6) S.Bywater and E. S. R. Steacie, ibid., 19, 326 (1951). (7) B. C.Roquitte, J. A p p l . Opt., 6,415(1967).
