15123-00-9Relevant articles and documents
Photoinitiated H- and D-atom reactions with N2O in the gas phase and in N2O-HI and N2O-DI complexes
Boehmer, E.,Shin, S. K.,Chen, Y.,Wittig, C.
, p. 2536 - 2547 (1992)
Reactions of H atoms with N2O have two product channels yielding NH + NO and OH + N2.Both channels were observed via NH A3Π X3Σ and OH A2Σ X2Π laser-induced fluorescence spectra.Photoinitiated reactions with N2O-HI complexes yield a much lower / ratio than under the corresponding bulk conditions at the same photolysis wavelength.For hot D-atom reactions with N2O, this effect is somewhat more pronouced.These results can be interpreted in terms of entrance channel geometric specificity, namely, biasing hydrogen attack toward the oxygen.Another striking observation is that the OH and OD rotational level distributions (RLD) obtained under bulk conditions differ markedly from those obtained under complexed conditions, while the NH as well as the ND RLD are similar for the two environments.In addition, OH Doppler profiles change considerably in going from bulk to complexed conditions, while such an effect is not observed for NH.The changes observed with the OH RLD are most likely due to OH-halogen interactions and/or entrance channel specificity.Under bulk conditions, the Doppler shift measurements indicate a large amount of N2 internal excitation (i.e., ca. 25 000 cm-1) for the OH (Υ = 0) levels monitored.This is consistent with a reaction mechanism involving an HNNO intermediate.The hot hydrogen atom first attaches to the terminal nitrogen of N2O and forms an excited HNNO intermediate having a relatively elongated N-N bond compared with N2O.Then the H atom migrates from nitrogen to oxygen and exits to the N2 + OH product channel, leaving N2 vibrationally excited.A simple Franck-Condon model can reconcile quantitatively the large amount of N2 vibrational excitation.
Mechanistic Details of the Heterogeneous Decomposition of Ammonia on Platinum
Vajo, J. J.,Tsai, W.,Weinberg, W. H.
, p. 3243 - 3251 (2007/10/02)
Absolute reaction rates have been measured for the catalytic decomposition of NH3 and ND3 and for the NH3 + D2 exchange reaction over a polycrystalline platinum wire at pressures between 5 x 10-7 and 0.5 torr and temperatures between 400 and 1200 K in a continuous flow microreactor.At relatively low pressures and/or high temperatures, a primary isotope effect was observed for the decomposition of ND3, indicating that a surface reaction involving N-H bond cleavage is the rate-limiting step.Under these conditions, the order of the decomposition reaction is unity with respect to ammonia pressure with an apparent activation energy of 4.2 kcal/mol.A coverages increase, corresponding to relatively high pressures and/or low temperatures, the order of the decomposition reaction is zero with respect to ammonia, and the reaction rate becomes controlled by nitrogen desorption.In this case the apparent activation energy of the decomposition reaction is 22 kcal/mol.The kinetics of the NH3 + D2 exchange reaction have been used, together with data concerning the adsorption-desorption parameters of NH3, H2, and N2 as well as the reaction intermediates NH and NH2, to develop a mechanistic model which descibes the reaction rate over a wide range of experimental conditions and which includes the energetics of each intermediate step in the decomposition reaction.This model is discussed in terms of a potential energy diagram for ammonia decomposition on platinum.
