Pressure Influence on the Rate of NF3 Decomposition Behind Shock Waves

Abstract

The rate constant of the NF3 dissociation reaction in a helium mixture in the low-pressure limit P < 1 atm. was directly measured in a shock tube by a UV absorption method. The rate constant may be expressed as K = 1014.38±0.07 x exp {-[36600 ± 2100(cal/mol)]/RT}, cm3/mol.s in the temperature range T = 1050–1600 K. Levels of the NF3 stationary dissociation fraction were also measured as a function of the initial temperature of the mixture behind the reflected shock wave. It increases monotonically with temperature and reaches 50% of the value at 1600 K, which corresponds to high NF2 concentration up to 2 x 1017 cm-3. Rates of NF3 thermal decomposition in the temperature range 1950–2050 K and pressure range 1.2-4.2 atm were also measured. The bimolecular rate constant of the NF3 decomposition reaction depends strongly upon pressure. An empirical formula was obtained from the experimental data which correctly expresses the dependence of the measured rate constant of decomposition upon the temperature and pressure of the reacting mixture behind the shock wave.