Shock wave study and theoretical modeling of the thermal decomposition of c-C4F8

Abstract

The thermal dissociation of octafluorocyclobutane, c-C₄F₈, was studied in shock waves over the range 1150–2300 K by recording UV absorption signals of CF₂. It was found that the primary reaction nearly exclusively produces 2 C₂F₄ which afterwards decomposes to 4 CF₂. A primary reaction leading to CF₂ + C₃F₆ is not detected (an upper limit to the yield of the latter channel was found to be about 10 percent). The temperature range of earlier single pulse shock wave experiments was extended. The reaction was shown to be close to its high pressure limit. Combining high and low temperature results leads to a rate constant for the primary dissociation of k₁ = 10^15.97 exp(−310.5 kJ mol⁻¹/RT) s⁻¹ in the range 630–1330 K, over which k₁ varies over nearly 14 orders of magnitude. Calculations of the energetics of the reaction pathway and the rate constants support the conclusions from the experiments. Also they shed light on the role of the 1,4-biradical CF₂CF₂CF₂CF₂ as an intermediate of the reaction.