A DIRECT MEASUREMENT OF THE REACTION NH3-]2NH(2)(NH)

The reaction of NH in its electronic ground state with ammonia was inv estigated behind incident shock waves using narrow line width absorpti on detection of NH(X(3) Sigma(-)). The initial concentrations of HN3 w hich was used as source of NH(X(3) Sigma(-)) were very low in order to reduce the influence of secondary reactions. Thus it became possible to measure kinetic data for the reaction of NH(X(3) Sigma(-))+NH3 (1) directly. In a temperature range from 1300 to 1700 K a rate constant k (1) 10((14.5+/-0.3)) exp (-(112+/-9) kJ mol(-1)/R T) cm(3)/mol s was o btained. The apparent energy of activation fits well into an Evans Pol anyi plot for H abstraction reactions of NH(X(3) Sigma(-)).