Elementary Reactions of NH2 in the Gas Phase

The elementary reactions of NH2 are divided into N-H-, N-H-0-, N-H-C-, and N-H-C-O-containing systems and systems in which other elements are involved. 

The recombination of H atoms with NH2 (la) is expected to be the dominant reaction pathway at high pressures [2, 3], whereas the reaction channel (1b) is important at high temperatures. At low pressures reaction (la) is of minor importance [4 to 8] as observed in the flash photolysis of ammonia. In the pressure range 330 to 2020 mbar the recombination channel (la) was studied by pulse radiolysis of NH3 [5] kia was found to be in the fall-off region at these pressures. The rate constant at zero pressure was determined to be kia(0) = 2.2x 10 cm mor s (M = NH3). The high-pressure limit kia(oo) seems to be too high with respect to the results obtained from the reverse reaction NH3- NH2 + H, the thermal dissociation of ammonia. 

Using the ESR and LMR detection techniques for H, D, and NH2, a room-temperature rate constant of k = (3.2 0.8) x 10 cm mol s was obtained for the isotope exchange reaction NH2 D- NHD H [9]. This value is expected to be equivalent to the high-pressure limit of reaction (la). 

The reaction NH2 +D2- NHD +D was measured in an isothermal flow reactor [26] under pseudo-first-order conditions ([NH2]o [02])- the temperature range 639 to 1140 K a rate constant of k(T) = 2.9 x 10 exp[-(47.6 2) kJ morVRT] cm -mol s was obtained. Direct measurements of the kinetic isotope effect gave k(H2)/k(D2) = 3.3 at 740 K and 2.4 at 1140 K, indicating that tunneling significantly contributes to the reaction [26]. 

The reaction of N atoms with NH2 has several exothermic pathways  

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