Effects of the third body (O and N) on the recombination of molecular nitrogen using quasi-classical trajectory methods

Abstract

The investigation of the recombination reactions poses significant challenges due to the complexities involved in three-body collisions including simultaneous interaction of three bodies and multiple time scales. This work aims to investigate the complex dynamics involved in the recombination of atomic nitrogen to form molecular nitrogen using the quasi-classical trajectory method for the N3 and the N2O systems. The recombination pathways considered include a single-step direct reaction and a two-step mechanism that involves the formation of an intermediate with a finite lifetime which is stabilized through a subsequent collision with a third body. The latter is further classified as Lindemann or Chaperon mechanism based on the role played by the third body. The model uses a time-lag parameter to allow for a consistent treatment of all the reaction pathways. It is observed that the recombination probability is greatest for collisions involving low translational energies and low time lags. Recombination rate coefficients are evaluated using a novel rate coefficient expression developed for three-body collisions. Low temperature recombination rate coefficients, which can be computationally prohibitive to evaluate using traditional detailed balance methods, can be evaluated at a low computational cost. The recombination pathways are determined algorithmically by identifying the various interaction time scales. The direct mechanism is found to have a larger recombination probability, but a lower rate coefficient. The effect of the third body (oxygen and nitrogen atoms) on the recombination dynamics is explored in detail. It is observed that the recombination in excess of O atom leads to a larger population of the low internal energy states, as opposed to recombination in the excess of N atoms. The dominance of the Chaperon mechanism is seen in both systems.