Computation of quasiclassical trajectories by symplectic algorithm for the N(⁴S) + O₂(X³Σ_g^-) → NO(X²Π) + O(³P) reaction system

Computation of quasiclassical trajectories for the N(⁴S) + O₂(X³Σ_g^-) → NO(X ²Π) + O(³P) atmospheric reaction system, based on a new ground potential energy surface reported by R.Sayós et al., has been performed in this work by means of both the fourth-order explicit symplectic algorithm (S4) and the fourth-order Runge-Kutta scheme (RK4), and then computed results of two schemes are compared. It is shown that RK4 cannot preserve energy conservation and symplectic structure of the reaction system, which results in the bad veracity of the trajectory calculation. RK4 cannot rightly reflect both the colliding mode and the reaction mode of the trajectories. Moreover, the amplitudes of vibration of the reactant molecule and the product molecule become gradually small with the time increasing, and their rotation-vibrational levels in fact vary during the integration. For these reasons, RK4 cannot assure the accuracy of the quasiclassical trajectory (QCT) study of the atmospheric reaction. However, S4 maintains these characteristics and can actually describe the circumstance of the reaction system. S4 is better than RK4 is prospective in the QCT study of the chemical reaction.