The gas phase association of CH3 with the HAr2 cluster to form a vibrationally/rotationally excited CH4* molecule is used as a model to study microscopic solvation dynamics. A potential energy surface for the reactive system is constructed from a previously fitted H + CH3 ab initio potential and 12-6 Lennard-Jones Ar-Ar, Ar-C, and Ar-H potentials. Classical trajectory calculations performed with the chemical dynamics computer program VENUS are used to investigate the CH3 + HAr2 → CH4* + Ar2 reaction dynamics. Reaction is dominated by a mechanism in which the CH3 "strips" the H-atom from HAr2 during large impact parameter collisions. For a large initial relative translational energy the CH3 + HAr2 → CH4* + Ar2 cross section is the same as that for H + CH3 association, so that HAr2 acts like a "heavy" H-atom. However, at a low initial relative translational energy, the long-range Ar2-CH3 attractive potential apparently makes the CH3 + HAr2 association cross section larger than that for H + CH3. Partitioning of energy to the CH4* and Ar2 products is consistent with a stripping mechanism. The initial and final relative translational energies are nearly identical and the CH4* rotational energy is controlled by the initial CH3 rotational energy. The velocity and orbital tilt scattering angles, θ(vi, vf) and θ(li, lf), respectively, are consistent with the stripping mechanism. On average only a small amount of the product energy is partitioned to Ar2 vibration/rotation and CH4* + Ar2 relative translation.
|Number of pages||9|
|Journal||Zeitschrift für Physik D Atoms, Molecules and Clusters|
|State||Published - Mar 1992|