Ultraviolet absorption was used to measure the rate of formation of difluoromethylene (CF2) from decomposed CF3I, C2F6, and CF4 in excess argon behind shock waves. In some experiments pure CF4 was shocked Data were taken over a temperature range from 1700° to 3000°K at total concentrations between 2(10−5) and 5(10− 6) mole cm− 3. A chemical, nonequilibrium shock-tube computer program was developed to analyze the CF2 kinetic profiles. By curve fitting the data, rate constants for a number of fluorocarbon reactions are obtained.

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Ultraviolet absorption and mass-spectrometric observations of shocked C2F4–Ar gas mixtures have indicated that the C2F4 monomer exists in thermal equilibrium with CF2 radicals and that the initial C2F4 oxidation mechanism involves two steps C2F4→ lim Ar2CF2CF2+O2→CO+2F+O.Dissociation and oxidation rates were determined from uv absorption measurements of CF2 at 2536 Å behind incident shock waves. The C2F4 dissociation reaction appeared to be second order, 12d[CF2]/dt=kAr[C2F4][Ar], with kAr=7.82×1015T12 exp(−55 690/RT) cc/mole·secover the temperature interval from 1200° to 1800°K at total concentrations between 0.9×10−5 and 1.7×10−5. A least-squares fit to the experimental equilibrium constants for the reaction C2F4=2CF2, using the integrated form of the van't Hoff equation, yielded logKc=−69 432/2.303RT+4.62 (Kc in mole/cc).From the measured heat of reaction, the heat of formation of CF2 at 298°K was calculated to be −39.7±3.0 kcal/mole. Mixtures of C2F4 and O2 in varying mole ratios were allowed to react at temperatures between 1500° to 2500°K with molar concentrations of reactants ranging from 4×10−8 to 6×10−7 mole/cc. The oxidation reaction was observed to be first order in both CF2 and O2, d[CF2]/dt=−kox[CF2][O2], with kox=2.92×1010T12 exp(−13 280/RT) cc/mole·sec.

The thermal decomposition of CHF3 has been studied in excess argon behind incident and reflected shock waves over a temperature range from 1600° to 2200°K at six total pressures between 0.29±0.03 and 28.2±1.6 atm. Direct mass-spectrometer analysis of the reaction mixture showed HF and CF2 to be the major decomposition products. Kinetics for the reactionCHF3→ lim ArCF2+HFwere determined spectrophotometrically by observing the rate of formation of CF2 in absorption at 2536 Å. The decomposition reaction was first order in CHF3 concentration and dependent on total concentration. The high-pressure limiting rate constant is given by k∞Ar=(7.03±0.70)1011exp[(−58 400±2200)/RT]sec−1,where 58.4±2.2 kcal/mole is considered to be the minimum energy E0 for dissociation. For the lowest pressure 0.29 atm, the reaction is interpreted by a second-order mechanism, d[CF2]/dt=k2[CHF3][Ar], with the rate constant expressed as k2Ar=(2.05±0.14)1035T−5.75±0.23exp[(−58 400±2200)/RT]  cc mole−1·sec−1,indicating in terms of the classical Kassel theory the participation of 7.25 effective oscillators for the dissociation of a critically energized CHF3 molecule. Taking E0=58.4±2.2 kcal/mole as the heat of reaction at 0°K, the heat of formation of the CF2 radical is −40.2±4.0 kcal/mole.

The thermal decomposition of the difluorocarbene radical diluted in argon has been studied behind incident shock waves over the temperature range from 2600 0 to 3700 0 K at a total pressure around 0.5 atm. The progress of the reaction has been followed by monitoring the time rate of change of CF2 molecules in absorption at 2536 A. The observed rate data for the disappearance of CF2 are interpreted by the dissociationrecombination mechanism, -d[CF2J/dt=kt[ArJ[CF2J -kr [CFJ[FJ[ArJ, with kj = (4.20±0. 67) 1()26 r-2 . sa ±O.62 exp (-106 OOO±5700/ RT) cc/mole·sec, k r = (6. 57±1. 79) 1()26 r-2 . sa ±O.62 cc 2 /mole 2 ·sec. Experimental equilibrium constants based on the reaction, CF 2 = CF + F, are calculated and fitted by the van't Hoff equation, yielding -103 OOO±5700 10gK. 2.303RT 0.41±0.11 (K.inmole/cc), for the temperature interval between 2600° and 3500°K. From the heat of reaction (107. 3±5. 7 kcal/mole) and the heat of formation of CF2 ( -39. 6±3 kcal/mole) at 298°K, the heat of formation of CF at 298°K is estimated to be 49.2±8. 7 kcal/mole.