Direct measurements of the reaction NH2+H-2 -> NH3+H at temperatures from 1360 to 2130 K

The reaction NH2 + H-2 --> N-3 + H (11) was investigated behind shock waves in the temperature range from 1360 to 2130 K. Time histories of NH2 were m easured by frequency modulation (FM) spectroscopy. The rate constant was de termined to be k(11) = 4.5.10(13).exp[-61 kJ mol(-1)/RT] cm(3) mol(-1) s(-1 ) (Delta log k(11) = +/- 0.15, Delta E-a = +/- 9 kJ/mol). According to recent literature values the reverse reaction NH3 + H --> NH2 + H-2 (-11) can be described by k(-11) = 1.5.10(7).T-2.0.exp(-47 kJ mol(-1) /RT) cm(3) mol(-1) s(-1) for the temperature range of 400 to 2500 K. On the basis of k(-11) and by using the enthalpy of formation of Delta(f)H(298)(0 ) (K)(NH2) = 190 kJ/mol, which was determined in a previous study [1], via detailed balance the following expression for the forward reaction (11) was obtained for a temperature range of 400 to 2200 K: k(11) = 1.5.10(4).T-2.6 .exp(-25 kJ mol(-1)/RT) cm(3) mol(-1) s(-1). This expression is in very goo d agreement with the reported experimental values for k(11).