Re-evaluation of rate constants for the reaction N₂H₄ (+ M) ? NH₂ + NH₂ (+ M)

Rate constants for the dissociation/recombination reaction N2H4 (+ M) -><- NH2 + NH2 (+ M) are determined by a combination of quantum-chemical calculations and statistical unimolecular rate theory. Between 1100 and 2500 K, limiting low-pressure rate constants for hydrazine dissociation in the bath gas Ar of k(0) = [Ar] 6.1 x 10(20) (T/1000 K)(-7.3) exp (-34490 K/T) cm(3) mol(-1) s(-1), limiting high-pressure rate constants of k(infinity) = 7.6 x 10(16) (T/1000 K)(-1.0) exp(-33600 K/T) s (-) (1), and center broadening factors of the falloff curves (between 1100 and 1600 K in Ar) of F-cent = 0.71 exp(- T/1460 K) + 0.29 exp(- T/21 K) + exp(-13400 K/T) were calculated. Using equilibrium constants K-C = 1.7 x 10(3) (T/1000 K)(-1.5) exp(-33,460 K/T) mol cm(-3), between 300 and 600 K limiting low-pressure rate constants for the reverse recombination of NH2 radicals in the bath gas N-2 of k(rec,0) = [N-2] 4.4 x 10(20)(T/400 K)(-6.9) exp (-1630 K/T) cm(6) mol(-2) s(-1), limiting high-pressure rate constants of k(rec,infinity) = 4.4 x 10(13) (T/1000 K)(0.44) exp(-140 K/T) cm(3) mol(-1) s(-1), and center broadening factors (between 300 and 600 K in N-2) of F-cent = exp(- T/1130 K) + exp (-10340 K/T) were obtained. A comparison with experimental results for hydrazine dissociation from the literature suggests incomplete falloff extrapolations toward k(infinity) and experimental problems in the determination of k(0) at temperatures above about 1600 K. Implications of the present re-evaluated rate constants for the modeling of high temperature ammonia oxidation kinetics are discussed, showing an only small influence of their precise values on the overall properties of the process.