Communication: Equivalence between symmetric and antisymmetric stretching modes of NH3 in promoting H + NH3 → H2 + NH2 reaction

Abstract

Vibrational excitations of reactants sometimes promote reactions more effectively than the same amount of translational energy. Such mode specificity provides insights into the transition-state modulation of reactivity and might be used to control chemical reactions. We report here a state-of-the-art full-dimensional quantum dynamical study of the hydrogen abstraction reaction H + NH3 → H2 + NH2 on an accurate ab initio based global potential energy surface. This reaction serves as an ideal candidate to study the relative efficacies of symmetric and degenerate antisymmetric stretching modes. Strong mode specificity, particularly for the NH3 stretching modes, is demonstrated. It is further shown that nearly identical efficacies of the symmetric and antisymmetric stretching modes of NH3 in promoting the reaction can be understood in terms of local-mode stretching vibrations of the reactant molecule.

Full dimensional quantum mechanical calculations of the reaction probability of the H + NH3 collision based on a mixed Jacobi and Radau description

“…The probabilities of the symmetric and asymmetric stretching excitation states are very close especially in the energy region below E tot < 0.6eV . Our present result are coherent with the results of Song et al 31 in which the excitation of the two stretching states are nearly equivalent in promoting the reaction.…”

“…Here, the two eigenstates are not perfectly degenerate with our basis set. However, following the work of Song et al 31 , we can obtain the average probabilities of those degenerate states that are also given with a star in the Fig. 3.…”

“…al carried out a new calculation based on this PES with the Yang's full dimensional method. 31 In this paper, we propose a new full dimensional method for reactive systems with five atoms. We use a description based on a successive separation into subsystems with polyspherical coordinates 32 , more precisely two Radau vectors and one Jacobi vector for reagent NH 3 and one Jacobi vector for the incoming hydrogen atom.…”

Recent advances in quantum scattering calculations on polyatomic bimolecular reactions

“…The dynamics calculations on the PIP-NN PES can provide more trustworthy results and predictions. Very recently, the reaction dynamics and mode specificity of the H+NH3 reaction were investigated on the PIP-NN PES using the full-dimensional (9D) ISSWP method 179 . It was shown that the symmetric and asymmetric stretching excitations greatly enhance the reactivity, and the efficacies are nearly equivalent, as shown in Fig.…”

Ab initio thermal rate coefficients for H + NH3 ⇌ H2 + NH2

“…In this work, we calculate the thermochemistry and the thermal rate constants for the similar H + NH 3 ⇌ H 2 + NH 2 reaction using the same theoretical approach as that taken previously . The H‐abstraction reaction H + NH 3 ⇌ H 2 + NH 2 has been fairly well studied both experimentally and theoretically . In addition, a nine‐dimensional global potential energy surface of NH 4 and quantum dynamic calculations have been reported .…”