First-Principles Simulation of Highly Reactive Systems: Immediacy on a Femtosecond Time Scale

Abstract

Using Car-Parrinello molecular dynamics we study the first reaction steps of the decomposition of a nitrogen-rich molecule and of a mixture of molecular oxygen and molecular hydrogen. Using the simulated-annealing approach we increase the temperature of the systems till they start to react. Both systems have in common that they react violently and that the precise reaction pathways, respectively the single reaction steps under the chosen conditions are largely unknown. While the first system decomposes completely within some hundred femtoseconds, the latter mixture reacts only partially on this timescale due to entropy. Complex reaction chains involving up to ten hydrogen and oxygen molecules allow for a fast reaction, but require a very specific arrangement. To our knowledge such reaction chains of neutral, stable, ground state molecules were not described before. The hope for a decomposition to nitrogen respectively to water is essentially fulfilled, but side products are observed.