A direct measurement of the reaction NH₃ + NH→2NH₂

Abstract

The reaction of NH in its electronic ground state with ammonia was investigated behind incident shock waves using narrow line width absorption detection of NH(X3X-). The initial concentrations of HN, which was used as source of NH(X3C-) 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(X3X-)+NH3 (1) directly. In a temperature range from 1300 to 1700K a rate constant k , = 10(i4.5t0.3)exp(-(112t9) kJ m o l~' / R T ) c m 3 / m o l s was obtained. The apparent energy of activation fits well into an Evans Polanyi plot for H abstraction reactions of NH(X3X-).

Combustion Chemistry of Nitrogen

“…An estimate for this rate coefficient obtained with the DHT method of Section 2.4 is seen in Figure 2.30 to be similar in magnitude and temperature dependence to their data. It is also consistent with the rate coefficient for the reverse reaction reported by Rohrig et al (1994). We recommend that the Davidson et al expression kJ7e = 5.0 x 1Q13 exp(-5000/T) cm 3 mol-1 s-1 be used for this rate coefficient.…”

Progress and Prospective of Nitrogen-Based Alternative Fuels

“…By monitoring the concentration of NH rate, Röhrig et al were able to measure the rate coefficient of NH 3 + NH . When comparing their derived coefficient for 46 above 1500 K to that suggested by Davidson et al, good agreement was observed . Fagerström et al found that the rate of NH 2 recombination has only a weak temperature dependence at low temperatures (200–400 K), in agreement with Khe et al (300–500 K) and Patrick et al (272–348 K) .…”

“…The coefficient suggested by Cohen does not seem to agree at any temperature with any of the other values (Figure a), which is understandable considering the assumption made in assigning its kinetics . While Röhrig et al measured the reverse reaction, calculating the rate coefficient of eq from their data yields the only direct measurement of this reaction. The resulting values are in good agreement with both the Xu et al and Klippenstein et al rate coefficients at 1290–1711 K, as is the fitted coefficient by Davidson et al at 2200–2800 K (Figure b).…”

“…Therefore, it is more likely that the main recombination channel they observed was eq and that their inability to measure changes in NH 3 and NH circumvented detection of the more commonly assumed secondary pathway (eq ). Xu et al determined that rate coefficients calculated using CVT/SCSAG with MP4 level of theory for eq had the best agreement with the coefficients suggested by Cohen and Davidson et al ,, Konnov and De Ruyck assumed eq to be the dominant recombination channel based on the measurements of Stothard et al and the rate of eq they extrapolated from the results of Röhrig et al Despite the difficulties mentioned above in the results of Stothard et al, Konnov and De Ruyck achieved good agreement with experimental results when modeling N 2 H 4 decomposition . Klippenstein et al calculated the high- and low-pressure limit rate coefficients for eq and the coefficient for eq employing CAS+1+2+QC­(8,8)/CBS//CASPT2/aug-cc-pVTZ level of theory .…”

“…While Davidson et al fitted only the rate coefficient of the eq recombination channel in their simulations, they reported that inclusion of the other pathways did not affect their simulation results . By monitoring the concentration of NH rate, Röhrig et al were able to measure the rate coefficient of NH 3 + NH . When comparing their derived coefficient for 46 above 1500 K to that suggested by Davidson et al, good agreement was observed .…”