C2F4 Dissociation in Nitrogen Shocks

A kinetic study of the tetrafluoroethylene—difluorocarbene radical reaction was conducted in excess nitrogen behind incident shock waves over the temperature range from 1200° to 1600°K at total gas concentration around 1.25×10⁻⁵ moles/cc. The rate of formation of CF₂ was observed spectrophotometrically and is reproduced by the rate law $$\frac{1}{2}\mathrm{d[}{\mathrm{CF}}_2{\mathrm{]/dt=k}}_f[{\mathrm{N}}_2\mathrm{][}{\mathrm{C}}_2{\mathrm{F}}_4{\mathrm{]-k}}_r[{\mathrm{N}}_2\mathrm{][}{\mathrm{CF}}_2\mathrm{][}{\mathrm{CF}}_2]$$ with $$k_f^{{\mathrm{N}}_2}{\text{=(4.08±0.72)10}}^{40}{T}^{\text{−6.36±0.55}}\exp \text{[(−74\hspace{0.17em}900±3000)/RT]\hspace{0.17em}}\mathrm{cc}/\mathrm{mole}·\sec$$ and $$k_r^{{\mathrm{N}}_2}{\text{=(2.05±0.47)10}}^{38}{T}^{\text{−6.36±0.55}}\exp \text{[(−1840±263)/RT]\hspace{0.17em}}{\mathrm{cc}}^2/{\mathrm{mole}}^2·\sec .$$ Comparisons between the tetrafluoroethylene—difluorocarbene thermal‐equilibrium constants in N₂ and Ar shocks indicate that N₂ is vibrationally unrelaxed during chemical relaxation. The temperature determined from the chemical equilibrium constant and the time to reach 0.98 chemical equilibrium after shock compression are used to calculate the N₂ relaxation time. The results show that N₂ vibrational relaxation in the 1:100 tetrafluoroethylene—nitrogen mixture is about 10 to 50 times faster than in pure nitrogen.