Cluster impact chemistry. High-energy collisions of I2ArN clusters with a Pt surface

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Abstract
In this paper, we explore cluster–surface impact induced dissociation of an I2 molecule initially embedded within an I2ArN (N=11–553) cluster, which collides with a Pt surface. Molecular dynamics simulations of high‐energy I2ArN–Pt surface collisions (with initial center of mass velocities v=0.2–10 km s−1 and initial kinetic energies E0K=1 eV−1.2×104 eV) provide information on the yields and time scales for energy acquisition by the cluster and by the surface and energy deposition to the guest molecule via the formation of an intracluster microscopic shock wave, as well as on the I2 dissociation dynamics. The intracluster shock wave is characterized by a temporal peak in the cluster potential energy and in the saturation of the cluster temperature, with the sum of the yields for potential and kinetic energy deposition into the cluster being 0.5–0.6. The cluster residence time (τ=50–800 fs over our velocity and cluster size domain) coincides (within 20%) with the time scale for the cluster energy acquisition, decreasing linearly with v−1 and obeying a dynamic size equation τ∝(N+2.9)1/3. The characteristic time tp for energy deposition to the I2 molecule via a local mechanism involving pair interactions is also close to τ. The initial cluster kinetic energy dependence of the dissociation yields YD of I2 reveals a gradual increase of YD towards unity above a threshold at the energy Et. For smaller (N=11,53) clusters, Et/N is close to the dissociation energy of bare I2, while for larger clusters Et exhibits an exponential N dependence. Cluster impact dissociation of I2 in I2ArN results in higher YD values (≳0.4) than the high‐energy collision of bare I2 with the Pt surface for which YD saturates at 0.35. The I2 dissociation times 〈τD〉, which were characterized by averaging over the first passage times for the attainment of the turning point of the I–I intramolecular Morse potential for reactive trajectories, fall in the range 170–800 fs, exhibiting a marked inverse kinetic energy dependence, revealing an increase with increasing cluster size and obeying the rough relation 〈τD〉≂2τ, i.e., being proportional to the cluster radius. Energy acquisition and dissociation times are comparable to...