| Classical trajectory simulations were used to study Ar+CH4/Ni{lcub}111{rcub} collision-induced desorption and compared with experiment. Overall the simulation and experimental desorption cross sections are in excellent agreement, except at small incident angles &thetas;i (with respect to the surface normal) and low initial Ar translational energies, E i, where the simulation cross sections are approximately a factor of 2 too large. Direct collision between Ar and CH4 contributes to the desorption most. Excitation of the CH4 vibrational modes is negligible and CH4 rotation receives less than 10% of the available energy. Most of the available product energy is partitioned to CH4 translation and to the Ni surface and Ar atom. The CH4 translational energy distribution is multimodal and its peaks may be associated with trajectories in which the Ar atom rebounds off or sticks to the Ni surface and collisions in which Ar strikes CH4 with small and large impact parameters.; Ab initio direct dynamics classical trajectory simulations were performed to study gas phase SN2 reactions. For the Cl −+CH3Cl system, strong barrier recrossings were observed as in a previous study. Simulation of the OH−+CH 3F system shows that it is not sufficient to probe the reaction mechanism by simple a ‘visual’ inspection of the potential energy surface. There is a detailed relationship between the efficiency of energy transfer and the time scale for the reaction to proceed.; The unimolecular dissociation of C2H5F was studied using the direct dynamics method. The product energies, the energy partitioning mechanism of the barrier excess energy, and the correlation between the HF vibration and the products' relative translation and rotation are studied.; Comparison of the quasiclassical and Wigner sampling of initial conditions on the reaction dynamics was carried out for the Cl−+CH 3 SN2 reaction, H2CO unimolecular dissociation and C2H5F unimolecular dissociation dynamics. The simulation results show that unlike photodissociation dynamics, differences in the product energies caused by using the quasiclassical and Wigner sampling approach is not important for such reactions.; A simple QM/MM model was developed and tested for the [Cl–C 2H5–Cl]− transition state. Good agreement between this model and the ab initio results for harmonic vibrational frequencies indicates the validity of the QM/MM model. |
