An investigation of temperature and pressure dependence of the reaction of CF₂ClO₂ radicals with nitrogen dioxide by flash photolysis and time resolved mass spectrometry

Abstract

Abstract Rate coefficients of the termolecular reaction were determined over the temperature range of 248–324 K and at pressures from 1 to 10 torr by time resolved mass spectrometry. CF 2 ClO 2 radicals were generated by flash photolysis of CF 2 ClBr in the presence of oxygen. Their rate of decay was measured by following (CF 2 O 2 ) + fragment ions formed in the ion source. With 2 to 40 mtorr of NO 2 present the dominant removal pathway is addition to form the peroxynitrate. The third order rate coefficients are wholly within the falloff over the experimental pressure range, and have a negative temperature coefficient. Rate constants for the reverse reaction, the unimolecular dissociation of CF 2 ClO 2 NO 2 , D. Koppenkastrop and F. Zabel, Int. J. Chem. Kinet. , 23 , 1 (1991) were employed to calculate equilibrium constants, from which a 600 torr value of the combination rate coefficient was obtained at each temperature. From the temperature dependence of the equilibrium constants, the average enthalpy of reaction over the experimental temperature range was found to be 106.1 ± 0.3 kJ/mol. Extrapolation of the combination rate constants to lower and higher pressures, and estimates of low and high pressure limiting rate coefficients, k 0 and k ∞ were done by nonlinear least squares fit of the experimental data, using the empirical F c equations developed by Troe.