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 12d[CF2]/dt=kf[N2][C2F4]−kr[N2][CF2][CF2]with kfN2=(4.08±0.72)1040T−6.36±0.55exp[(−74 900±3000)/RT] cc/mole·secand krN2=(2.05±0.47)1038T−6.36±0.55exp[(−1840±263)/RT] cc2/mole2·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.