Direct dynamics classical trajectory simulations of the O+( 4S) + HCN reaction at hyperthermal energies were performed based on the ground state PM3 potential energy surface, and the results have been used to interpret guided ion-beam experiments. This simulation exemplifies the complex chemistry and dynamics that can happen in hyperthermal ion-molecule reactions. Calculations were carried out at various collision energies ranging from 2 to 15 eV with emphasis on energies higher than 5 eV. All the energetically accessible reaction channels were found, including the HCO+/HOC+, NO+, and CO+ ions reported in the experiment. OCN + and CN+ were found to be negligible at high energies. Relatively lightweight ions, NH+, CH+, and OH+, which are energetically accessible on both quartet and doublet potential surfaces but which were not reported in the experiment, are found to have cross sections below 1 Å2. The calculated excitation functions for NO+, HCO+, and CO+ agree with experiment qualitatively with quantitative agreement for NO+. Cross sections for HCO+ and CO+ are consistently overestimated at high energies, which is attributed to the poor description of the repulsive part of the potential energy surface by the PM3 Hamiltonian. Product energy disposal and angular distribution reveal complex mechanisms for elimination, abstraction, and exit-channel charge transfer reactions. The angular distributions at high energies (>8 eV) are characterized by dominant forward scattering as a result of direct reaction mechanisms. Backward and sideways scattering at lower energies is due to the formation of very stable intermediate molecular ions. The agreement between simulation and experiment for cross sections and angular distributions, especially their dependence on the collision energy, suggests that the quartet ground state dynamics are dominant in high energy collisions.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Physical and Theoretical Chemistry
- Surfaces, Coatings and Films