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

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. Reaction mechanisms in highly reactive systems: The decomposition of crystalline C2N14 is compared to the decomposition of a supercritical mixture of hydrogen and oxygen. The formation of molecular nitrogen from C2N14 is immediate at high temperatures. In contrast, in the hydrogen/oxygen system, several hydrogen atoms have to attack the molecule simultaneously to break the oxygen double bond.