Shock-Tube Study of the Termal Dissociation of Nitrogen

Abstract

The dissociation of nitrogen behind shock waves has been studied over a temperature range of 6000 to 10 000°K. A time-resolved Mach-Zehnder interferometer measured the density profiles in the reaction zone. Rate expressions based on classical collision theory and the hydrodynamic constraint equations were used to fit the experimental profiles. Inferred rate constants are presented with N2, N, Ne, and Ar as third bodies. This work differs from previous studies of nitrogen in that a measurement of the forward dissociation rate was made in N2 with N2 as the third body and in that the new data indicates that N is about as effective a third body as N2. Vibrational relaxation data indicates that to a first approximation there is no significant coupling between vibrational relaxation and dissociation over the temperature range covered. Vibrational relaxation times in N2-Ne mixtures behind combustion driven shocks indicate that Ne is about 1.4 times as effective as N2 in vibrationally exciting N2, agreeing well with predictions of the Landau theory. This agreement between theory and experiment is just as good as that obtained for Ar utilizing pressure breaks, vindicating the combustion technique.