Study of 2-H-Heptafluoropropane and Its Thermal Decomposition Using UV Photoelectron Spectroscopy and ab Initio Molecular Orbital Calculations

The thermal decomposition of 2- H -heptafluoropropane, CF 3 CHFCF 3, at low pressure, heavily diluted in argon, has been studied over the temperature range 600−2000 °C using photoelectron spectroscopy. Comparison of the results obtained has been made with results of recent electronic structure calculations of possible decomposition pathways and results of a shock tube study. The most favored reaction thermodynamically, to produce CF 3 CF═CF 2 + HF, is found to be the main decomposition reaction at lower temperatures, 600−900 °C. At higher temperatures, 900−1200 °C, the decomposition reaction to give C 2 F 4 + CF 3 H was found to become important. No evidence for CF 3 CHFCF 3 → CF 3 CHF + CF 3, a reaction expected to be important from a shock tube study, performed at much higher pressures, or for CF 3 CHFCF 3 → CF 3 CF + CF 3 H was obtained, although for the latter reaction it is likely that CF 3 CF converts into C 2 F 4 under the conditions used before photoionization, in the ionization region of the photoelectron spectrometer. At higher temperatures C 3 F 6 decomposes to C 2 F 4 + CF 2, and C 2 F 4 decomposes to CF 2 . Ab initio calculations have been performed of the adiabatic and vertical ionization energies of possible primary pyrolysis products to assist assignment of the photoelectron spectra recorded for heated flowing gas samples. A comparison is made between the threshold photoelectron spectrum and the photoelectron spectrum of CF 3 CF═CF 2